Personally, I enjoy UT3 a lot. The style of play and movement is different than in the 03-04 versions, but it kinda has the feel of the original to me. The UI is a dumbed down version to make it ps3 compatable. (I hate consoles!). The gameplay is very fast and there is more and more user created content popping up every day. Also, unlike say Crysis, you dont have to have a monster system to play it. Runs great on my E4500@3.0 with 2 gigs of ddr2 800 and an 8600gt. This is a game that will be around for a while and will only get better with time. I believe I seen it at gogamers(?).com for like $29US.
I play it alot, so I would say it is worth it, but I am an avid UT player. My opinion may not be what you are looking for. Try the demo beta. If you comp can run it with everything all the way up the game looks great. If not, it can run well on just about anything, but it will look terrible on lower end machines. (if that matters to you, just thought I would let you know) Hope this helps!