Definitely worst game in the series aka what the hype can do
Plus it wasn't even done by the original team if you check these pages, as Onslaught was first planned as mod for UT2003:
http://en.wikipedia.org/wiki/Unreal_Tournament_2004
http://liandri.beyondunreal.com/Unreal_Tournament_2004
But the game is more low paced than UT2003, has bad changes, even graphic side, is badly optimised, has worse GUI and everything, not that it isn't easy to configure, it is, but to what extent, to have crappy blue childish crap and windows everywhere.
The music is worst of the series, in exception of few tracks and the old ut2003 ones, which I don't count as new in this game.
The Skaarjs and new characters are very noobishly done as well. They don't have even own voicepacks and the alien2 used first intended for genmokais is unused as well, it would help if at least skaarj's voices were pitched or altered old ones through script, as it was with UT goty's skaarj hybrids.
I can only agree with reviews like that of Talonfire on the editor choice edition page, because it actually tells truth about the game.
And the singleplayer, god that has to be one of my most awful gaming experiences, I didn't even beat the last boss without cheats and I had the most powerful out of three (there are three bosses: Malcolm, Xan and Clanlord). But the map you get to play him is overscaled version of original hyperblast map from UT, really overscaled and with useless weapons such as grenade launcher and with the opponent who kills you with three bullets. The tourney itself is some kind of mix between UT2003 and UT2003 beta style (which had more sports feeling with challenges through game and credit system), but really badly done. So nothing new at all.
The gore of this game is really laughable and hands down to UT3 for bringing back some violence back, beacuse I don't feel like playing with child weapons, which ut2004 ones remind most, not to mention sniperrifle zoom sprite and maybe sound are taken from unreleased Unreal Warfare title, which eventually became gears of war. But this UT2004 sniperrifle doesn't have animations to speak of, the reload sound makes you feel you reload it, but you don't see a thing like that, you don't even see your hand.
And the new maps, Curse4 is really insult and I don't see why they didn't leave Curse3 from UT2003 in there, it was much nicer map to look at. Most of the new maps have terrible layout and washed out graphics, the exoerience of them is as of some half life deathmatch maps and deathmatch in HL was always the worst thing. Same goes for ctf and BR, the old stuff what was fun in ut2003 is now damn boring and new maps are not any good.
So what is left is the rest of mods, Invasion can be fun, but is inbalanced in this game and the enhancing invasion mods are not worthy either. They could have imporved the invasion a bit, but they didn't. Then, the new modes we have is Assault and Onslaught, these are most fun and have the highest artistic value in them in some sort, but can still become boring. Assault is just like enhanced gametype from original UT, where you need to achieve objectives in certain timeline as attackers and the opposite team tries to stop that from happening. Plus now you have controlable vehicles and turrets in the maps to help you.
Onslaught is a battle with vehicles about dominating points on the maps, the power nodes, by taking control of them and link them to central enemy power core, you can then destroy and win the game, but ONS is still unbalanced when there is only one node left, it is most likely your destruction. By taking each powernode you gain more weapons and vehicles which are bound to the each powernode. That's it, as for the vehicles, they feel very unrealistic and overpowered against players, Unreal 2 expanded multiplayer has really realistic vehicles compared to this and was the first Unreal game to introduce vehicles and radar and not UT2004 as many think. Not to mention U2XMP has a real radar, but that's not what I am going to talk about here.
Another low point of this game is bots, they are very unbaknced and behave weird, even comapred to ut2003 ones, which were fair to what difficulty you set them and not so unbalanced and dumb and causing game lag.
The funny thing is that perhaps the best deathmatch map in singleplayer, deck17, is originally a custom map for UT2003 and even that one is better with its own music and not the KR crap and also with jumpboots.
The only really great thing about this game is that in instant action you can configure it to more playable game via mutators and you can download lot of content, I found most fun the vctf gametype online (which is unused gametype in the game), although bot pathing at these new maps suck as the authors didn't know how to make them go around, but not all of the downloadable content is good, some are pretty overrated trash mods, well you have to choose carefully, but there are some real gems out there.