UT3 as a PC game isnt bad at all, but as a UT game it was disappointment. Imagine the same game with a completely different name which has no relevance to an Unreal game, all of a sudden your not so let down because unlike if it were a UT game it doesnt have to meet any of the expectations a UT game might have, instead it would only have to meet the expectations of your average PC game today. Unfortunantly it is a UT game and has alot more to live up to then just good controls, interface, and great support.
In summory it meets the PC needs but not UT needs.
From my standpoint, UT3 disappointed me all on its own. I didn't play the other UT games, so had no preconceptions of what to expect. I didn't find Q4 SP all that bad either. It wasn't spectacular, but it wasn't total crap either. I think the problem most people had with the multiplayer was that they expected it to be Q3 and it wasn't. By the time they worked it around to be very similar it was too late and most of the potential players had moved on.
I wasn't any more let down from UT2k4 to UT3 as I was from UT to UT2k3 really... They both sucked compared to the original but I wasn't gonna lose sleep over it as I wasn't a huge player of those games.
UT was a fantastic game and the assault mode alone wasted so many hours of my life. Finding out that the assault mode was totally gone in UT2k3 and they replaced the sniper rifle made me cringe...
To be fair the Unreal series has 99% of the time been a pile of wank anyway. Why is it so hard to make an ACTUAL sequel, rather than change all but the name. I want a next gen sequel to the first Unreal... I can imagine it being stunning...