I think it all depends on what the DLC has to offer and price(which in most cases is a matter of opinion)
for example, no way in hell would I pay $10-$15(maybe even more) for something like capcoms' street fighter IV costumes sets when they do nothing to enhance the game(from a gameplay perspective)
but for games like ME2 where the DlC adds much more content to the game without taking away from the game itself; like in the OP's case where he a actually had to buy the DLC to play the game in its entirety.








