Making Achievements

Nice little article/interview about developer insights into making achivements.

http://www.gamasutra.com/view/feature/3976/unlocking_achievements_rewarding_.php?page=2

I like Infinity Ward's "evenly spread" approach. Make some achievements easy, tie them to game progress, then have some that require a bit of knowledge about the game your playing, then make some for the hardcore gamers that will put some time into the game, the upper 25%.

"The trick is you want to constantly feel like you're being rewarded," says Bowling. At least 60 percent of achievements should be achievable by the average player on one play through. That's why COD4 has achievements for consistent headshots and knife throws -- it rewards players for developing their skills.
                  - Robert Bowling, community manager at Infinity Ward