Focusing on 5d2 via live mode and 10x zoom is a joy, just can't say enough good things

If you get why those are great things, you need this lens.

really cool thing about this lens is that you can create quite some personalized photos

Crazy sharp (as has been said many times here) and compared to the 17mm this thing is easy to focus

F stop - depth of field: this is the most important thing

This thing is a beauty