I finished the "100%" achievement in Bully over the weekend.  It's not a particularly hard one to get 100% at compared to some other games out there (like GH3 with it's abysmal achievement design).  But it was a first for me.  A few other games I thought I would come close -- I'm still plugging away at Orange Box and Oblivion.  Most games I have put perfect completion simply out of reach, either by having a multiplayer component that just doesn't fit with my time availability, or by having ridiculous difficulty requirements. 

Much like game difficulty itself, I think that there is a general bias towards making these things too hard.  The "currency", as it were, is already devalued heavily by sports games or games like Avatar that give you 1000 /1000 trivially.  So what's the harm in letting a dedicated, but not insanely awesome, player of your game achieve full completion?

I admit I'm constantly battling between my feeding my Achivement addiction and trying not to let it steer me into just plain un-fun territory.  So I'm plinking away at 5-starring more songs on Guitar Hero 2 and 3 because that's a happy middle ground for me -- I like playing the game even though I know realistically I'll never 5-star Raining Blood or Psychobilly Freakout on Hard for either game.  But playing the game without sound, or not using the guitar controller?  What's the point of that.

Rock Band's "World Tour" mode was an excellent case in point on that.  When the game shipped, my wife and I played a lot of it, and pretty quickly hit the limit of the # of fans we could get at the "Medium" difficulty level.  If I encouraged her to play at Hard, it just wasn't any fun.  So our progress was stymied.  Fortunately, Harmonix recently patched it so that you can get more fans (and thus access more venues) at Medium.  I still hope we'll move up to hard eventually, but now at least we can move forward.  It's all illusory of course -- nothing prevented us from playing those same songs in Quick Play mode.  But context is important...