If you don't feel like watching the 2h 30min video Q&A, I pulled the youtube transcript and summarized it (used AI to help with formatting):

Key Concepts

• Scope of 0.5 is intentionally a "template patch." GGG bundled the endgame rework + a full crafting league to lock in what an endgame league should feel like in PoE2. Smaller incremental patches couldn't have set that template.
• No new class/weapon in 0.5. A class takes longer than one cycle. The interim leagues between 0.5 and 1.0 will be "month-long event" style, so balance fixes can ship without mid-league nerfs.
• Runes of Aldur = a craft-economy ecosystem, not just a mechanic. Every league must now contain something a player can grind for indefinitely. Aldur layers rune inscriptions on remnants → harder monsters → better loot, plus alloy/rune/forging benches and unique modification.
• The Atlas is now a fixed map of Wraeclast, not a procedural blob. Landmarks (league hubs, the central Fortress) sit in physical locations; you can pick any compass direction and hit content within ~4 maps.
• "Fortress" as a quest-driven pinnacle path. ~300 fortress nodes vs. ~150 atlas points; auto-completion exists so the fortress doesn't become a chore. Completing it ≈ Atlas completion in PoE1.
• Atlas Masters replace the monolithic Atlas tree. The big tree is now fully allocated by default; per-map "Master loadouts" carry the choice-based knobs (e.g., shrines on bosses for harder/more reward).
• Runic Ward = a sub-life trade-off resource. Powers the new colorless Kalguuran skills that work across classes and use level (not attribute) requirements.
• Leech rewrite — single source + damage cap on the leech calculation. Goal: doubling leech% should actually double recovery; damage past a threshold no longer feeds infinite recovery for meta-skill triggering builds.
• Defence buffs from Act 3 → early endgame. Player EHP at midgame is well below GGG's spreadsheet target; armor/evasion bases, hybrid clusters, and deflection scaling are all being raised.
• Quitting points are a design goal. Endgame now has progress bars and clear completion goals so players know when to step off — a direct response to the "400 hours played, terrible game" Steam-review pattern.
• Pinnacle boss attempts are now infinite once the fragment is earned (across the board, not selective like 0.4).
• In-game build planner ships in 0.5, with one-click import from community sites (also unlocks console build sharing). GGG explicitly will not ship official build templates.

Detailed Analysis

Why this expansion is so big

In retrospect Jonathan thinks a smaller patch might have been wiser, but the goal was to deliver a single patch that defines what an endgame league looks like in PoE2. The previous endgame had no goals — players hit maps, didn't know what to do, and quit. By shipping all the league reworks, the Atlas overhaul, and Aldur together, GGG sets a "this is the bar" template. The team building campaign acts is largely separate from the team doing balance/systems, so the act content for 1.0 is on its own track in parallel.

Runes of Aldur deep-dive

• Remnants are the league's atomic unit. You inscribe runes on them; each rune adds monster modifiers (harder = more rewards) and feeds a recipe pool that determines the loot.
• Recipes have hidden internal logic (e.g., iron-themed runes feed iron-themed crafts) — most players will treat it as a pick-from-list interface, but designers built recipe families.
• Olroth's Legacy rips a modifier off a Kalguuran unique and turns it into a unique rune you can socket into items of the same class.
• Meta-craft runes can be inserted, used to roll mods, then "popped out" by a different rune. Mark cites this as a more legible take on PoE1 meta-modding.
• Bonded modifier system: every new rune participates in the existing Shaman "bonded" framework, including (intended) the unique-derived runes.
• Grand Expeditions (formerly log books) let you sail a tile-grid ocean of unique islands with handcrafted oddities. Tablets buff islands; some log books reveal pinnacle-relevant zones.
• "Power runes" are tier-2-of-everything rare drops; some appear in the campaign too (e.g., bow rune granting +50% chance for an extra arrow).
• 160 total runes; alloy crafting added on top. Multiple full crafting benches were built to ~80% then cut for time.
• The crafts are deliberately scoped per slot (Breach = jewelry/caster/minion focus, Aldur = weapons/armor with runes) so you don't have to learn every system to gear every slot.
• Kalguuran uniques can be transformed at the Verisium bench — a hybrid base might split into ES, evasion, or strength variants. Targeting "3 outcomes per Kalguuran unique."
• Runic Ward is a sub-life pool under normal HP. Designed so it's strictly additive in early bases (no trade) but trade-off in endgame bases (more ward = less other defences). Hand-rolled per base type ("a metric ton of metadata"); not a formula.
• Kalguuran skills: weapon-agnostic, no attribute reqs, level-gated only; spend Runic Ward instead of mana. ~25 in this batch with room to grow.

Plus Skill Levels & Rarity

Trimming top-end +skill rolls and shifting some of the high tier up the mod ladder rather than removing it. Rarity is still slated for replacement long-term; in the interim, GGG wants leagues to be "more economically targetable" so players can chase the loot type whose price has spiked.

Balance & Meta — economy as a design lever

Mark frames PoE1's resilience: when currency price rises, players farm currency-leaning mechanics, dragging it back. PoE2's blanket Rarity boost broke that signal. Letting tablets/league-tree picks bias reward type restores the lever. Greater/Perfect orbs (especially Perfect) drop too easily — transmute and augmentation drop rates will be reduced. Mage Blood teased to exist but not described.

QoL drops

• Build planner ships in-game; community sites can produce "one-click import" links (no manual file copying — important for console).
• Mouse+keyboard / controller hot-swap is "the running joke" but Jonathan pledges it lands this league.
• Visibility / particle bloat acknowledged as a real problem (e.g., explosive grenade screen-fill); fix is artist+engine+balance triage, not a transparency slider — Jonathan refuses sliders because they "ruin something fundamental."
• Steam Deck Verified status targeted for launch; UI scaling overhauled across panels. Endgame perf still rough on Deck.
• Campaign signposting: zones reshaped so monster types funnel you toward objectives (snakes head toward the Venom Crypts; humanoids cluster near the shaman boss room). Some areas were un-linearized to make wayfinding the speedup, not raw size.

Skill levels in the campaign

Some "main-skill" gems sit too late. Jonathan's preferred fix is rearranging where skills are gained, not compressing the unlock curve.

Skills, Ascendancies & Builds

• New ascendancies (Spirit Walker, Martial Artist) hit a design problem: every existing beast needs a tameable counterpart, every glove mod needs an "alloy" version. Mark: "I'm so excited for how much work we've created for ourselves."
• Tame Beast damage roughly tripled internally; companion revive times raised so you actually feel investment in single high-impact pets vs. swarm builds.
• Martial Artist's Fists of Stone (gloves → fists) does affect unique gloves and explicit mods; rune/socketed mods generally stay as they are. Skill-granting unique gloves keep their skill — recreating skills for this case is "a line that has to be very special to cross."

Defence rewrite

Player EHP between Act 3 and early endgame is significantly below the team's spreadsheet target. Their fix is a buff campaign rather than nerfing monsters:

• All armor/evasion base types get more defence up to (but not including) peak endgame.
• Top-end outliers slightly trimmed so rares stay relatively meaningful.
• Deflection formula is being rebuilt — too rewarding for tiny investment, dead beyond that.
• Hybrid passive clusters are being filled in (the strength/dex border in particular).
• Energy Shield recharge is "too easy"; Ghost Dance + 1k ES outscales pure-evasion → being toned.
• Armor/ES has the highest death rate by 300% — Jonathan does not yet have the solution; flagged as the next priority.

Passive Tree

GGG isn't restoring life nodes to the tree (yet). Jonathan's argument: don't compromise the tree to paper over a defence problem; fix defences, runes, body-armor base types, and itemization-side recovery first. Tree work in flight: kill notable clusters that grant a stat but no armor/evasion, add hybrid notables for secondary defences, fill out ascendancy-class-adjacent "starter wedges" (which are richer than the empty-class wedges). He's confident a slice can be substantially fixed in a day per slice once they have time.

Fire / Ignite / Damage-over-Time

DoT is on Jonathan's "top-5 (now top-10) list to fix." Pure-DoT fantasy (e.g., Flame Blast → spreading wildfire ignite) is a goal, not a current reality. Hits-with-ignite-on-top is currently strictly better. Keystones, supports, and itemization to enable pure-DoT are sketched; expected to land in an interim patch before 1.0. Combat pacing: average boss kill for the actual median player is dramatically slower than streamer pacing implies (~119s on telemetry vs. designers' guess of ~8–20s). Direction: keep the spectrum, but make god-tier require real investment, not free.

Recovery & Leech rewrite

• Single-source leech. Only the largest hit feeds your active leech buff at any time.
• Leech damage cap. A capped damage value (number TBD — "maybe ~100k or ~1M") is what gets multiplied by your leech %. Above the cap, more damage stops adding recovery. This breaks the meta-skill recovery feedback loop ("3M% of life per frame from infinite triggering").
• No more leech resist by monster rarity (white vs. unique) — leech is now consistent across boss and trash fights.
• Instant leech largely removed (it bypassed the cap).
• Early-game leech values can be raised now that the cap exists, so investment matters earlier.

Temple going core

The "snake" temple strategy is being killed by an algorithmic fix: rooms that the system wants to delete but can't (because deletion would disconnect the temple) are now replaced with empty connector rooms. Snaking was producing "1000% unacceptable" item drops; GGG didn't mid-league nerf it because pulling the ladder up after early adopters feels worse than letting a strategy run out. Reward rooms post-architect get buffed; Atlas tree applies to the temple; the temple has its own quest line and atlas-mini-tree.

Endgame Deep Dive

• Atlas as actual world geography. A real map of Wraeclast — landmarks (league hubs, the Fortress, the ocean for Grand Expeditions) sit in fixed positions roughly matching the campaign's world. Sail far enough into the ocean and you can find Oriath — a pure Easter egg until acts 5–6 ship.
• No direction is wrong. Pick any direction off the starting ziggurat and within ~4 maps you hit a league content cluster. NPC quest markers spawn within 1–2 maps.
• Fortress = the new Atlas-completion target. ~300 nodes, ~150 atlas points behind it, all of them designed one-of-a-kind (so auto-completion does have a real opportunity cost). Completing the main quest line (Ziggurat → wall → middle → back) is ~45–50 maps if you path efficiently.
• Atlas Masters replace big sections of the previous tree. Each has a quest-line that unlocks rows of keystones; you select which master is active per map, like PoE1 map device options. Hilda hunts beasts; Doryani tracks corruption (his quest absorbs the old Doryani questline); Pharaoh, Jin etc. could become future masters as new themes ship.
• Atlas tree fully allocated by default. Tradeoff: punchier nodes (no fear of "wasted points in the wrong biome"), but no real "build" choice on the big tree. Build choice moved into per-map Master loadouts and the league sub-trees (Breach, Delirium, etc.).
• League integration with Atlas mechanics. Each league has an Atlas-active behavior: Delirium fog spreads spatially; cracks open across the Atlas in Breach; ride-of-the-nameless picks biomes; pinning a tablet locks a tile to one league (preventing other-league spawns).
• Co-op progression preserved. Fixed Atlas portions complete for the whole party; infinite-farm sections remain personal. Some league progression nodes intentionally don't auto-complete in groups so they don't rob loot.
• Pinnacles tier-restricted, not level-restricted. You can race straight to a pinnacle if you have the way-stones — infinite attempts per fragment.
• Quitting points by design. Progress bars on every league + Fortress completion + challenges give players a defined "I'm done with this league" exit. Stated goal: prevent the "400 hours, terrible game" review.
• Portals/revives: the team has multiple iterations of "minus 1 portal per N modifiers" + Master-granted extra revives + Atlas nodes; final rules slightly fuzzy in the live convo but a master-granted extra revive is in.
• Three Ascendancy Trials: not all in 0.5; both existing trials (and ideally the third) targeted to be "good" by 1.0. The third trial is a coin-flip for 1.0.

Boss design

• 15ish new bosses in 0.5. Jonathan's pick: the underground Ritual pinnacle (light-vs-darkness staging). Mark's pick: the new Delirium voiceline-finally-has-a-body boss.
• King of the Mist demoted from PoE1 pinnacle status to a campaign-side encounter — the bar for "pinnacle" has moved. The team feels Olroth and friends were just PoE1 ports re-skinned, and 0.5's bosses are the first batch made entirely under PoE2's evolved boss pipeline.
• How a boss gets made (Mark): three threads — narrative, art-driven, and mechanic-driven — and any can fire first. Concept artists have a constant backlog of unbriefed creature work. The Aldur expedition pinnacle started life as a random Act 5 mini-boss; designers re-themed it with Verisium limbs, tripled scale, and re-animated it. They confirm Delve will eventually return and are already commissioning Crystal King family/successor concept art.
• Rogue Exiles are getting buffed and gain a "nemesis" return-and-hunt mechanic.

Actionable Takeaways

For players planning around 0.5:

• Expect economic targetability: pick the league/biome whose tablet gives the loot type you actually need.
• Defences scale better mid-game, but ES/Ghost Dance hybrid stackers and high-end armor outliers are pulled down — don't lock plans around current top-end ratios.
• The leech overhaul means doubling damage past the cap stops doubling recovery — meta-skill triggering builds will need re-tuning; flat leech investment becomes more linearly valuable.
• The new Fortress is the real Atlas-completion goalpost (~45–50 maps to pinnacle on a beeline for an experienced player).
• One-click build import is real — when you bookmark a build, prefer creators who publish to a tool that adopts the in-game format.
• Pinnacle attempts being infinite per fragment changes farming math: no more over-preparing; first attempt is meant to be hard.
• Parry/evasion/strength outcomes via Verisium bench mean low-level uniques can graduate into endgame; collect Kalguuran uniques you'd previously have shelved.
• Plan multiple Atlas Master loadouts for different map types — that's where build choice on the Atlas now lives.
• The team is explicit that streamers ≠ average pace. If your boss kills are 30s, you're well above the 119s telemetry median; balance discussions are calibrated to that.