DLC is somethign that became insanely popular in the 7th generation but it has ended up being a double edged swords. On one end it is great for multiplayer games like Halo, Killzone, and Call of Duty so it keeps bringing you fresh experiences. On the other hand it has allowed developers to release unfinished games and DLC also has been over-priced more often than not.
DLC killed the expansion. Popular games used to get a few expansions, not they are more micro-sized bites and people claim the games were unifinished instead. While I agree that DLC has been highly abused by certain companies, it has not been by all of them.
I do however miss the good old fashioned expansion.