Jared Rea of GameTap has written a fantastic article about the gamerscore, and the problems that currently plague it.
Gaining achievement points should be a rewarding experience and while competing for them makes sense, developers run the risk of poisoning the online field for players. The recently released Turok encourages players to go online and defeat a single opponent multiple times in a row without touching anyone else, or better yet, to go through an entire match without killing anyone.
I feel that developers should not include online achievements at all. Gears of War and Perfect Dark Zero are two more games that have ridiculous online achievements that do nothing but hurt the overall experience. It's obvious that this is a problem when you watch a teammate avoid the competition simply to achieve 10 points on their gamerscore.
You can read the full list of online blunders here. Microsoft has an innovative system on their hands, but developers need to work harder to strengthen the quality of their achievements. The system is only going to get worse if the twiddle their thumbs.