I bought a USP 9mm some time ago and it has become one of my favorite guns.
It's already been mentioned about recoil, reliability and accuracy, and I concur. So I thought I'd mention a couple of other things.
If you get the standard trig. configuration, DA/SA, you can carry it C&L or with the hammer down. You can engage the safety first, and then do a press check. You can engage the safety first and then cock the hammer.
One thing that I noticed about the USP 9mm is that it has a little lighter recoil spring than most 9mms. That doesn't mean a lot, but it does mean you can do a one-hand press check without pressing the slide against anything and in fact I can actually rack the slide with one hand and charge the chamber - reliably. Of course that's not too important unless you only have one hand to work with, but it is a nice option.
I really, really like the unique ambi mag release. I like it much better that the thumb push button release. I generally operate it with my trigger finger.
It is a bit wide for me to carry IWB, but so is a Glock. Speaking of Glocks, the full size USP weighs just a bit over one ounce more than a G-17 so it carries light.
I have no trouble carrying it year round in an OWB holster and a tee with light vest in the summer and a jacket, etc. for cooler weather. It is almost exactly the same dimensions as a Sig 226, but maybe a 1/16" wider.
I also have the P2000 and I like it, it's got the same mag release, is a smaller more ergonomic gun, but mine is a LEM version so it's kinda hard to compare my USP to the P2000. But, I do like the safety options on the DA/SA and the way the trigger works. The LEM is a bit heavy on the trigger break and the my USP has a heavy DA trigger and a great SA trigger.