As far as multiplayer goes, I want one thing, and one thing only.
Full customization. Starting weapons, weapons on the map, weapon respawn times, map alteration, etc. If Gears 2 doesn't have fully customizable private player match type games, it might fail the multiplayer aspect. From all the news that came out about multiplayer ("moving" weapon spawns, flamethrowers, etc), I really don't think Epic is going to make enjoyable and fun pre set settings for ranked games.
As far as single player goes, I want it to be more "balanced". meaning, don't have bosses as easy as the corpser, and bosses as difficult as raam. And the levels in general should be about equal in difficulty to clear, save "unique" areas of the game (driving the Derrick for example).