Achievements are useless and have no place in single player games, but they are sort of interesting in multiplayer/MMO games where they give vanity items or bragging rights if nothing else, however mundane or easy they may be.
For instance WoW has an awful lot of mundane achievements, but when you get them they are publicly announced, a few "GZ"s pop in your guild chat, and for 15 seconds you are a somebody again. Now's the time to tell them they suck and you're leaving them!