I have had one for a few years now, I picked up my USP for $400, and after having it for a while there are things I like and don't like about it. I'd buy one again at that price but I wouldn't pay much more because of its trigger.
I like its reliability and soft recoil.
I like its capacity and the grip size isn't that bad, especially compared with a glock 21.
I like the quality of the machining
I don't like the fact that the trigger and hammer spur are polymer coated and rubber, respectively.
I also don't like that the safety/decocker is polymer. It's bigger than a steel part needs to be.
I don't like the polygonal bore, but that's because I shoot a lot of cast lead handloads
I don't like the diminutive frame rail inserts. It works so I guess that's just personal, but I'd prefer them to be more substantial.
The DA trigger isn't as bad as, say, a p64, but it's far from good. Useable but heavy and spongy because of the flex in the trigger. The SA trigger is mediocre at best with a lot of take up and creep.
So that's it, with new metal parts... A trigger, hammer, and safety...I'd really like this gun, but I can't fault it at all as is since I've never had a problem. It does what it does very well.
My main gripe is that trigger. The fact that it's both heavy and flexy makes for one of the worst triggers in my safe.