not to be a joykill, but i'm an advocate of the redundancy of "achievements." how can acheivements "extend and expand" gameplay when a vast majority of them can be 'earned' in the course of the game- also, since they can only be earned once?
the only achievements i can think of that aren't earned naturally in the game- Upgrading the Battletower to it's full potential, slaying all the Fortresses' generals, finding Michael's Raft, and killing the Killer Bunny.

just saying. If Larian wishes to do so, they will.