I have owned Canon's flagship EF 35mm F/1.4L lens for many years. It's unquestionably an excellent lens. But the fact is that I hardly ever use it. The reason is simple. For its bulk I could grab an excellent zoom (24-70mm, 16-35mm, or the 24-105) and get far greater flexibility, albeit at potentially some miniscule sacrifice to image characteristics in certain circumstances.
But I like 35mm on a full-frame camera, particularly my 5D. So I recently purchased this little guy mainly for use on my 5D as a general purpose, lightweight and compact 35 mm lens.
What a joy this little lens has been! First of all, its diminutive size and weight are delightful, particularly on such a light camera as the 5D. The lens is not technically a "pancake" design (why doesn't Canon make any?) but at 1.7" it's sure not too much longer than a pancake. It's also a featherweight, like most of Canon's standard EF line. While it does not have the heavy metal build of Canon's L lenses it also does not have their mass.
Beyond that, however, results are all that I really care about and this little lens produces results in spades. It's razor sharp, excellent contrast (to my taste), excellent bokeh, reasonably quick to auto focus and easy to manually focus (unfortunately, like Canon's other standard EF line it's not a full-time manual focus lens).
I could go on and on. But by now I'm sure you get my impression.
If you are looking for a relatively inexpensive and reasonably fast 35 mm lens for your Canon your search is over. At just over $200 this is it. Just buy it. Unless you're an obsessive purist (or camera gear snob) you're unlikely to ever miss the differences that the extra $900-$1,000 would deliver with the 35mm f/1.4L.