As a fan who's played them all, it's a decent entry though I found it a bit on the disappointing side. The jumps aren't as airy as they were before, the weapons take too long to fire, the complex yet nice graphics don't properly complement the very simple concept of the twitch-shooter, and it's generally slower than before. It certainly wasn't bad, and I liked Warfare mode, though it felt like a step backward from Unreal Tournament, Unreal Tournament 2003, and Unreal Tournament 2004.
On a side note, I'm not really alone in my opinions it seems. Each game mode (online) might have one full server and a few others populated, though it's basically barren. (My first online deathmatch saw me with twice as high of a ping and still winning the match despite joining several minutes into it, so they seem to play pretty bad, too.) In short, I'd rather get Unreal Tournament 2003 (where my clan specializes) and even Unreal Anthology, which includes Unreal Gold, Unreal 2, Unreal Tournament, and Unreal Tournament 2004, though you'll still have a lot of fun if you do go with Unreal Tournament 3. I did like its new version of UnrealED, though (same one I use with Gears of War).
Try the demos of Unreal Tournament, Unreal Tournament 2003, Unreal Tournament 2004, and Unreal Tournament 3 on FileFront and see which you prefer. (My personal favorite is Unreal Tournament 2003, though I love them all.)