I am (always will be?) a UT fan, from the original Unreal on. I have purchased them all, most on pre-order.
I find the game itself to be a solid progression from each previous one. Honestly, UT2k3 was the worst of all and 2k4 was a fix of all things broken in it w/ excellent additions by the time the EC version came out. UT3 was a good change in that it was not just a re-skinning of 2k4. Problem for some is that 2k4 was so good that what they seemed to really want was just that.
IMO it hearkens back to UT99 while keeping some playstyles of 2k4 and adding new aspects and a more diverse teamplay. It is fun. Yes, the sp campaign is laughable... but then each previous version was pretty lame on that as well so no worries.
Honestly, with all the negative press it got on release and all the ppl moving to consoles it is a true shame that there is not more of a community. The other versions still thrive but for "new" games UT3 has really suffered. Let it be known though, it is not for the lack of a good game as I think it is a ton of fun. The hoverboard added to onslaught (err, warfare) alone was brilliant. The other changes there, the orb etc are perfect additions to the game.
It is a fast paced and fun addition to the series that is one of the lost gems of PC gaming from the last year. Hopefully more will buy it as it gets cheaper so that the online community will grow and kick Epic in the backside for practically stating that they are backing away from PC gaming. (thereby killing any future sales of said games) But I digress... don't want to go into an anti-console rant.
basically, get the game. If you enjoyed the demo then you will have fun w/ it, even enjoy botmatches. There are still plenty of online games to get in on, just not as many as there SHOULD be.