Pokemon Infinity is a roughly 8-10 hour playthrough. It's fun, simple, and enjoyable. The plot is nothing special but it's good enough for the short runtime and honestly not a bad premise.
I really liked a lot of the new Mons and forms, but I wish some of them weren't as obscure to get and also that it was better informed in the game what pokemon got new evolutions etc.
The game has various difficulty settings, I played on Normal, which I think is perfect for if you want to nuzlocke. If you don't like nuzlockes but still want a moderate challenge, I'd probably go up a difficulty level.
I think the only "big" downside I can point out for the game is the last 10 minutes. It decides to get weird with the plot and pulls out some questionable tropes and cliches, with the last one being the most questionable and definitely going to annoy a lot of players, but it wasn't a big deal to me, it's just a pokemon game lmao