I don't like the new maps but my biggest gripe is that the playerlist. There are BARELY any people in that list and it's very hard to get into a game now. I want to get into the group that doesn't have the DLC because it's obvious that it is a much larger playerlist and I wont have to sit around waiting to get into a game.
Have you tried going to xbox360's system preferences and searching through the 'memory' tab? Find MW2 and sometimes DLC is a separate entity that you can delete.
edit: my bad, i thought i was in a different forum, obviously.