I broke down and bought it, and boy is it fun. More fun than TF2 or Crysis online or any other multiplayer. So much fun, that you spend half the game laughing in disbelief at your actions and the incredibly artistic visuals. The vehicle CTF is especially great and just a whole lot of fun.
The singleplayer is very half assed though. I mean it is basically like playing multiplayer offline with bots, which would be fine, except that there is a retarded storyline. Between levels of Death match, Team Death match, CTF, assault, and Vehicle CTF missions you are hit by cutscenes powered by really campy voice acting that feature an absolutely retarded storyline.
The singleplayer missions and the actual cutscenes feel totally detached from each other. It is like you are taking turns playing the various UT game modes with bots, and watching cut scenes explaining the storyline, without anything gelling the two. It is obvious that the a storyline was written to accommodate the standard UT offline gameplay, without any changes to the actual gameplay that would indicate the presence of a story.
Every time you unlock a new singleplayer mode, you watch a cutscene in the storyline where you listen to a laughably ridiculous explanation on a standard game mechanic. For example respawning has been explained as some new technology that allows your enemy to ressurect a certain number of times. Capture the Flag is actually you stealing some of your enemies tech., and then bringing it to your base (WTF?). Other game types have similarly stupid explanations.
Epic said they put a storyline together, because they found that 50% of all UT purchasers never played the game online. I think they should have done a proper story mode, like they did with Gears of War, instead of this. I am pretty sure that the game is poorer because of the singleplayer campaign, which really feels cheap.
Having said all that, playing online is amazing fun. The visuals are just top notch, and the engine scales beautifully. On my sister's 7950, the game still looks gorgeous, and better than its predecessor. The maps are all dripping with fantastic art, and some of the alien vehicles are just so sexy, it hurts. The vehicles add another dimension to the game. Mauling using the vehicles, or just using their speed or firepower brings a lot of joy.
Some of he weapons have been tweaked, and for the better. The Flak cannon and rocket launcher, while still really powerful, have been nerfed a bit. They've also made it more difficult to bunny hop.