Okay, before you come at me, hear me out.
I'm not saying it's all bad, like the newer seasons are actually enjoyable to watch with the Japanese dub, mostly. But the older episodes are just horrible and almost unwatchable for me with the Japanese dub. Japan made really good dubs in the past, like TTTE's Japanese Dub is legendary, so idk how this dub is so bad, but imo it is.
I do like the translations, but my main problem is with some of the voice actors. Not all of them, but some of them. I'll only be covering the main characters though.
- SpongeBob: He's one of the only characters to sound good throughout the series' run. Hiroyuki Tsuru mostly fit SpongeBob in the first three seasons and did a solid job at voicing the character, but my main problem with him, is how inconsistent he sounds. Like in S1, he was mostly consistent, giving SpongeBob an energetic, high-pitched, teenager-like tone, but in S2-S3 he kept switching between a high-pitched and very deep voice, and it got annoying how inconsistent he sounded, and sometimes he even sounded emotionless. Thankfully, Taiki Matsuno, who's the heart of this dub, did a way better job at providing SpongeBob's voice, and he's still the most iconic voice for the character for this dub. May he rest in peace. Kōki Miyata, the new voice for SpongeBob is actually REALLY good. He sounds really close to the voice Tom Kenny had in Season 1, and Miyata also sounds really similar to both Hiroyuki Tsuru and Taiki Matsuno, while also giving a fresh new voice, that just sounds cute, and would've fit the character from the beginning. Overall, SpongeBob was really well-casted in this dub.
- Patrick: Patrick's voice is what makes S1-S8 unwatchable fot me in the Japanese dub. Like what were they thinking? Ikuko Tani is a good voice actress, and did a solid job with Mrs. Puff, but her Patrick voice sounds genuinely awful and ear grating. I don't have a problem with Patrick having a less deep voice, but not to the extent of him sounding like an old lady. Like he sounds nothing like he should. And in S1-S3 it's especially annoying, since SpongeBob's voice is way deeper than Patrick's, which makes little sense. Now, I kinda think that Ikuko Tani's raspy voice would've fit SpongeBob, kinda. But not Patrick. Her voice as Patrick is awful, and not only because it's not what I'm used to, but it just doesn't fit the character in the slightest. Takashi Nagasako is hands down my favourite Patrick VA this dub, he gave a perfect, dim-witted and loveable performance, and gave Patrick the voice he should have had from the beginning. It's such a shame that his role as Patrick was so short-lived. Now, Mitsuaki Kanuka is definitely a different voice. He sounds deep and high-pitched at the same time, and he's an amazing Patrick. He keeps the same charm, that some may see in Ikuko Tani's performance, and his voice also resembles Takashi Nagasako, making him a perfect voice for Patrick. I'm so glad he replaced Ikuko Tani. So overall, Patrick was horrible before, but now he sounds pretty good.
- Squidward: Squidward imo is the character best portrayed in this dub. Rokurō Naya did amazing, and enough said about that. Yōji Ueda... literally sounds the exact same as Naya did in S1. I don't know how they found a voice actor who sounds exactly like Rokurō Naya, but they nailed it with Yōji Ueda, and he does an amazing job. Both of Squidward's VAs in this dub are top tier.
- Mr. Krabs: He had only one voice actor throughout, that being Keijin Okuda. I'll be honest, I wasn't a fan of his voice in the early seasons, he just sounded a bit weird, but he became really good later on, and he's still amazing. Glad he's still part of the voice cast, now that he's the only member left.
- Sandy: She sounds good. Yūko Ogiso is my favourite Sandy voice this dub, she sounds soft, her voice is nice to listen to, and despite sounding soft, she fits the character PERFECTLY. It's such a shame she quit. Chie Matsuura sounds good, but for me, she's a bit too high pitched, compared to Yūko Ogiso. Don't hate her voice though, because she's one of the highlights of this dub.
- Plankton: For fans who don't like Plankton's voice in this dub, you've probably been waiting for this. Last and probably least is Plankton. His voice is just... I don't like it. I see what they were trying to do, by kinda making his voice match his size, but the reason it just doesn't cut it for me, is because Plankton's deep voice is supposed to be an irony, of how he has a small size, but a big ego and a deep voice. And let's be honest, while Plankton is mostly a comedic villain, that doesn't mean he's not a threat. And giving him a voice like this, totally undermines the fact that he's supposed to be threatening. Yūko Ogiso and Chie Matsuura both had emotions for sure, and probably did the best they could with the dubbing direction given, but they are both just so unsurprisingly bad as Plankton. Chō is literally the only VA for Plankton I think fit him.
- Karen and Pearl: Both were voiced by Ikuko Tani, and I think they sounded too old, didn't like their voices. Rie Takahashi did a much better job with their voices imo.
- Mrs. Puff: Now in her case, I find Ikuko Tani to be better, as she fit her better. Rie Takahashi is good, but her voice is a little too young for Mrs. Puff.
The male incidentals are mostly dubbed by women too, which is really annoying, because then what's the point of male and female fish having distinct designs to tell their genders apart, if all of them have the same voice? In newer seasons, their voices are better imo.
TL;DR: Not a fan of the Japanese dub overall, but it def got better.