As far as L lenses go, this is the 3rd most important lens you should get, with the Canon 24-70 2.8L being the 1st, and the Canon 70-200 2.8 IS L II being the second. More on those later.

The 16-35mm 2.8 is a MUST have general purpose wide angle lens for any kind of serious professional use. Whether you are shooting, events, sports, wedding, landscapes, even certain types of portraits, it is very, very versatile and pretty good in low light at a max aperture of 2.8.

One negative is that you will see distortion and some vignetting in the corners, otherwise, it is a GREAT lens.