There is very little fault you can find with this lens. If I have to think of one, it's the purple fringing at wide apertures, and well, the price. When shooting high contrast scenes, you will see PF but stopped down to around f4 or f5.6, it's negligible. As for the price, I think it's crazy, especially after Canon has increased the price recently. A new 35mm f1.4L now costs more than $1700 CAD, plus taxes. I am happy to say that I bought it used at a very good price a few years ago.
So why is it so special? This is an all purpose lens that's good for any lighting. It's invaluable for low light. Easily one of the favourite lenses of the wedding photographers, especially on full frame. Even in good light, like most Canon L lenses, this lens renders pictures beautifully with great colour and contrast, not to mention that this is one very sharp lens! I find that pictures comes from this lens has a certain3-D effect to them. This lens focuses with lightning speed and is silent, thanks to the UltraSonic Motor used.
A while back, I did a comparison with the Canon EF 35mm f2 and this lens. You can check it out here. The f2 version performed admirably, but once you put them side by side, the physical difference is huge. Optical quality aside, the 35mm f2 feels toy like with plastic built, and weighs next to nothing (this could be a good thing -- light weight is good.) The 35L is by no means small, but it's the smallest of the Holy Trinity and not really that heavy. I can hand hold it with my 1D Mark II all day without problems. I sold the f2 version and kept the 35L. Why? The 35L instills confidence. Holding it in your hand, you know you can count on it when you need it. And, if you can't take good pictures with this lens, you know you have no one else to blame but yourself :)
Click on the pictures to see a larger version:
One of the very first few pictures I took with my 1Ds when I bought it at Henry's Outlet Store -- 1Ds & EF 35mm f1.4 @ f1.4
Motor Bike -- Canon 20D & EF 35mm f1.4 @f2.5
Megan -- Canon 1D & EF 35mm f1.4 @ f2.5
Ryan at music recital -- 1D & EF 34mm f1.4 @f2.2