The 2021 TV series is excellent and this is more or less a recap compilation movie of it, plus a little bit at the end that shows us what happened next after the original's potentially dark ending.
To my surprise, I was disappointed. It isn't bad, but I wouldn't recommend it.
The format is a TV documentary. Unknown filmmakers are interviewing lots of characters from the Odd Taxi TV series. (Afterwards? Or just near the end? It's unclear.) The interview segments are new scenes, but they're just a bunch of framing stories and nothing actually happens in them. They provide a bit more insight into the characters and that's all.
The meat of this film is a compilation of the TV episodes... but I thought it was missing something important. The TV series can sometimes be hard to watch, because its characters are capable of being so stupid and/or focused on terrible goals. I don't mean that in a bad way. The show's a study of some of the most blind, delusional and/or just plain self-destructive behaviour that human beings can focus on, especially middle-aged men. It's like watching someone slit their wrists in slow motion, for twelve episodes. (Intermittently. In between all the cool or funny scenes.)
This film doesn't really do that. It's just retelling the core story. It's about the plot. It's quite a deft condensing, admittedly, and perfectly watchable, but it's lost most of that "oh my God stop it stop it". It's still irritating to watch, say, Kabasawa and his quest for social media followers. The film reminded me of how painful these idiots can be... but it didn't make me feel the pain.
The film also assumes you've seen the original. It doesn't even bother trying to preserve secrets and surprises, with characters mentioning key story points in their interviews. (Even the fact that they're still alive to do interviews in the first place is a sort of spoiler, although you'll start noticing after a while that not all characters have appeared yet.) There's no attempt to hide Yano's identity. We're told everything immediately with Shirakawa. This makes sense for viewers who know the original, but I'd strongly advise against watching them the other way around. If you're thinking of watching the TV series, avoid this film until afterwards. You wouldn't even save much time by watching the film instead. It's over two hours long, i.e. almost half the original's total running time.
Its postscript is huge, though. It tells us what happened next. This is nice to see... but it doesn't really contain any surprises. You'll watch it once, nod to yourself and then never need to see it again.
It's still Odd Taxi, though. It's clever and quite fun. Odokawa made me laugh, in his melancholic deadpan way. "You're wasting your time on pointless stuff, aren't you?" I've been griping and grumbling, but this is still a much better film than most, animated or otherwise. You could do a lot worse. Just don't expect a sequel. It's a retelling, or a "reconstruction" as the producers called it.