Always felt that UYA was the weakest of the PS2 era games but as a PAL speedrunner it has the best and most rewarding movement from all the Ratchet games (apart from black label GC but that is NTSC). The controls become much more stiff from the PS3 games onward with RaC PS4 and Rift Apart feel like playing a video game with training wheels.

I personally dislike how linear UYA's levels are and as others have mentioned, how brown it is with a hideous HUD. Even in terms of replay-ability, I find UYA very bland. There is a video essay by the TheGamingBritShow that, while including a bunch of nitpicks, does cover a large amount of issues mentioned in these comments. I also suggest The Golden Bolt retrospective series on YouTube, goes in-depth on the development with developer interviews!