If someone told me about the Xbox 360 achievement list feature before I tried it, I would say this would be a nice feature to have but would probably not pay too much attention to it. Now after trying it, I can honestly say that this little feature was, in my opinion, one of the most brilliant features added to the system. Granted it does not really make sense without all the other related aspects of the console: great games, unique account throughout games, a really impressive integrated online experience. I mean, the concept of the achievements is really addictive if you just play offline, but it becomes incredibly addictive associated with online and your friends list. It's the boasting rights of proving you've done it in a game, it's the inherit competition aspect of comparing your achievement score to your friends or just the fun of knowing what your friends have played and how well they are doing at it.
Achievements are also a great way to have you really enjoy the games you play. A typical before-achievements experience could be to go through a game to get to the final screen. Achievements will probably get you to explore the little cool aspects of a game that you would not otherwise explore. A nicely sketched out achievement list for a game will point out the cool things in the game and will leave you playing the extra hours thus taking much more out of a game.
This has been, so far, kind of an exclusive experience for XBox 360 owners but that is about to change. PC owners will get to enjoy the addictiveness in new Windows Live games (even if they go for the free account), PlayStation 3 will get to enjoy a similar thing via their Home online offering although I'm not sure about this last one, the beauty of the XBox 360 achievements is in part how simple they really are!
It does seem like achievements are here to stay! So..be an achiever!
Here is my gamercard...in case you want to compare your achievements to mine! ;-)