I enjoyed U2 quite a bit but I could see why some gamers, especially those who don't care much for high production values, didn't find it particularly impressive. Though much improved from the first game, combat elements such as control, hit-detection, AI, etc, are still B level at best. The platforming is even more lacking. It's fun to watch Drake perform his acrobatic feats but actually controlling him in those segments isn't particularly fun or challenging.
In terms of story, U2 started off pretty well but the big revelation was just as disappointing as the first's. Given the premise of the story, I had expected a lot more from the twist.
All in all, U2 was still a very enjoyable experience but the gameplay had ways to go before it was on par with the graphical polish.