The original UT is still the best, probably, but UT3 is a close second. It has that "feel" of UT, just not the polish. If this game (or the expansion, if they end up making one) gets the polish like 2k4 got over 2k3, I expect a great game.
As it stands, 2k4 was fun, for about two years, and then everyone began to realize that all you needed was good hitscan aim to win and the game degenerated into a laserfight that made it horribly unfun and dull to play. Which is probably why I stuck to ONS and vehicular gametypes - a couple guys with lightning guns are, for the most part, negated in that.