I'll start
Fallout Equestria:
-Velvet Remedy is a good and interesting character, definitely better than Calamity
-Homage and Red Eye are wasted potential and criminally underutilised as characters. I feel like Homage only exists to >!give Littlepip a girlfriend!<and the author is too comfortable sidelining her more interesting traits. And Red Eye is probably my favourite villain from this universe, but he still should have gotten way more page time.
-after building up Red Eye and the Goddess for so long, it felt wrong to >!kill them off so quickly and have the Enclave be the main villains!<
-Litllepip >!escaped from Fillydelphia!<way too easily
-having the entire final battle >!happen offscreen !<was a terrible fucking decision
-Too many flashbacks! Too many memory orbs!
Project Horizons (disclaimer- I'm only past book 3)
-Rampage is consistently insufferable and annoying. Every time the characters have a heart-to-heart, you can count that bitch to barge in, say dumb edgy shit and ruin the tone.
-Boo is an unnecessary character that contributes nothing to the narrative (at least so far)
->!the author coming up with an excuse to genocide Stable 99!< was a cheap and lazy move, it would've been more interesting to leave it intact and opposing the protagonists
-Goldenblood kinda feels like a self-insert. ,,Oh hey look, it's my OC, he's very smart and dedicated and imaginative and morally ambiguous and can talk back to anyone, also >!Fluttershy loves him and they have a kid!<!"
->!Twilight x Big Mac!<is like... ugh, just why?
-Too many flashbacks! Too many memory orbs!