I usually just ignore them if they are just "beat this level. Now, do it quicker. Now, do it on a harder difficulty." However, if they encourage you to play the game differently, I'm all for it. But I will go on record as saying any achievement that requires you to spend extra money for a special controller on top of the game, or an expansion pack, can kiss my ass. That includes the "all instruments" achievements on Rock Band/RB2 and GH:WT. Just pisses me off. I can't sing worth shit, so I won't get a microphone, and that will always keep me from getting all of the achievements.