AMAZING contrast, color, and bokeh. I read MANY reviews before purchasing this lens. I sold my 70-200f4 IS which I loved (great lens) and bought this one. I feel the fixed focal length forces me to be more creative, which is what I needed. but wow, the contrast on this thing is INSANE. I literally thought i accidentally changed my in camera settings looking at my first shots with it. Colors are deep and vibrant. I've heard people rave and say this is the closest canon lenses get to ziess glass, and although i've never used a ziess lens, I can totally see a difference in my other lenses (35L, 24-105L, and my late 70-200f4 IS). Pictures with this lens just have a different feel to them. If you're debating on this lens just BUY IT. I think every canon user needs to at least try it out. Plus the resale value is very good that buying then eventually selling may be cheaper than even renting.
(I love this lens so much that this is the first online review i've written for ANY purchase I have ever made. People on the fence just need to know how wonderful this lens is. I use it on a 5DmarkII)