To be blunt, the full game is excatly like the demo, but with some more maps and Warfare (its ONS, but with hoverboards, an "Orb" that will instantly capture a node, and sometimes you can do stuff like blow up a barricade.. so ONS really).
Its no less or more, remember the 2k3 release? yeah, its that all over, no assault, a bunch of missing options, annoying bugs, but this time there's also a useless server browser, the Admin tools are severely limited, there's no anti-cheat (and several nasty hacks and bots are allready out there), and the game is unstable on many systems (crashes and freezes).
The gameplay is good though, it really is, but its just in a sorry state, and to many of us, despite beeing big UT fans, it is not worth playing in this state, others feel it is ok, but only the blindest of fanboys will tell you that it is satiesfactory.
So get it at your own risk, but my personal opinion would be to wait it out, and see where this is all headed..