I finally got my UT3-worthy comp up and running a few weeks ago, and I never thought I'd say this after the demo (which I played when it first came out on my old comp), but I'm definitely in the 'loving' camp.
The game is certainly rough around the edges, but at its core is the single greatest combat dynamic ever devised. Not oversimplified, not overcomplicated. Just extremely, viscerally, ridiculously fun. Every weapon is a joy to use, death is bloodily glorious, victories are adrenaline-soaked triumphs that leave you grinning for ages afterwards. UT2004 may be more the choice for the competitive scene, with its defensive gameplay offering that extra element of skill, but it can't begin to rival the new game's sheer thrill.
Also, barring Crysis which requires NASA hardware to run properly, I reckon this is the best-looking shooter around at the moment. Higher-res textures than Mass Effect, more beautiful environments than Gears of War and Bioshock. Some of these maps are just staggering.
What I don't like? Like I said, it's pretty rough around the edges, but the only significant problems for me are the vehicles (I've never really 'got' vehicles but for some reason I found them more tolerable in UT2004), minimal crosshair customisation and lack of Assault. But the crosshair issue is only problematic for me in Instagib games. Normal-weapons TDM and CTF in UT3 have been some of the best times I've ever had in an online game.