Achievments are one of the best moves Microsoft has ever made.

[DavesterBrrr]

I wish they would do more achievements like they did in Mass Effect.  Unlocking of an achievement granted you new bonuses/abilities (i.e - +5% xp per kill, etc...) on your next play through.  Less annoying Fetch achievements like "Find 100 flags" *coughAssassin's Creedcough* would be nice also :P