From the PlanetXbox360.com feature top list:
"With Gamerscore being awarded for doing various Achievements in games, the Achievement system on the Xbox 360 has not only brought back, but also evolved the concept of the classic video game high score. There are some ways Achievements are inane, don't get me wrong – depending on the game, some Achievements are either downright ridiculous or just plain stupid to get. But there are some Achievements out there that really do get the point of the Achievement system – certain Achievements that, when you accomplish them, really do give that feeling of accomplishment. These Achievements really do make you feel like you've done something truly awesome and badass. Ten such Achievements are listed below; if you really want to feel like a skilled gamer, and to see the Xbox 360 Achievement system at its finest, then I suggest going for these each and every one."