I love the USP Tactical, but it does have some things I don't like.
The trigger has an excellent SA trigger pull, but DA feels like a nightmare. If you accidentally pull on the trigger while the gun is on safe, it feels
very prone to breakage.
The polymer double stack frame is too wide for some people. They also don't feel easy to hold onto when you have sweaty hands. However, a Hogue grip fixes that quickly.
The rail is the "Universal Rail" which takes an adapter in most mounting situations. I'd hope that in the future, HK switches over to 1913 Picatinny rails like everyone else is.
I naturally like pulling the hammer back without racking the slide. HK's hammer is rather small, and hard to get a firm grip on when cocking.
I myself hate target sights on combat based pistols. I would much rather have the standard sights. If you do get the Tac, make sure you don't plan on shooting in low light as they're solid black.
It's a very bulky pistol. The extended and threaded barrel eliminates alot of holster options, but there are still plenty quality ones available. The pistol is also a little bit on the heavy side (especially for a polymer pistol), but that's all in the extremely heavy duty slide.
Besides that, the USP Tactical is a very well rounded pistol. I myself prefer a 1911 to my specs, but the Tac would be my second choice. It's pretty accurate, reliable, and not to ammo picky from what I've seen. I used to hate plastic guns as they felt like rickity little toys. The USP is a very quality built, stout handgun, even though it is polymer. In fact, the USP series are the only polymer pistols I will even acknowledge. I'm sure you will be satisfied with it's durability and accuracy. I don't like very many handguns, and the USP series is one of the very few.
With that said, my next handgun after my SA Operator, will be a USP40 Compact.