I think starcraft 2 has acheivments nailed down brilliantly. Near enough all of them you can get as a standard player, and very few of them require you to grind grind grind like the one mentioned above.
But, the best part about them is the way that they force you to change your game. By that I mean that they ask you to play a level in a way that prehaps you probably wouldn't have done in the first place.
Example: One level where you get a hero, if he dies its game over. So, at first I hid him in the back and did the whole level with normal units, with no risk ot the hero what so ever. Easy Mode!
The acheivment was get 50 kills with the hero. what! Mental! I had to take risks, I had to be clever and use mechanics I wouldn't normally use. I was experiencing the game in a new way, because I wanted that achievment. And such fun I had!
THAT is exactly what they should all be designed to do. Not make you play the game for longer, but to play it in a certain way that may be different, harder or easier to your current method. Acheivments can teach, entertain and add SUCH value to a game if done correctly.
I get that certain acheivments are aimed at a very small amount of people who will play the game relentlessly...that 72,000 kills one for example, how ever hard it is to reach, imagine the feeling when that little sign pops up saying Unlocked! Worth it? To some, maybe.