badon: I don't have UnderRali yet, so I might be a little clueless. Can someone explain to me why you would stop playing the game while you wait for an expansion? Is it because the expansion is expected to improve the base game?
Just like David says, above. The expansion won't change the beginning or the end of the game. What it will do instead is give a whole lot of new places to explore during the middle of the game. it will also add some new weapon types which will probably change up some of the way that gun and melee users play; and it will add a new school of psi abilities that's sort of meant to be a general buff for all possible builds.
If you do play through and finish the game, then when the expansion comes out you'll need to either revert to a much older save, or else start a new character. Otherwise you'll be running around in a game world that you've already beaten, looking for things to do (and out-levelling them by a good bit, likely).