For the past 9 months I've had the pleasure of owning the Canon EF 35mm f2 IS and it is now a lens I could never do without.
Being that it isn't an L lens, I wasn't expecting some rock solid metal construction and it surely doesn't have that. It does have a plastic build very similar to the 100L (without the weather sealing of course) which is quite solid and certainly doesn't feel cheap. I'm very happy with it, especially because of the effect it has on the lenses weight. If you want something lightweight you can carry around all day without hassle, this lens certainly fits the bill.
Focus is fast and very accurate, even in low light. I rarely have any issues and when I do, it is usually due to user error (I have quite shaky hands). The DOF wide open is very shallow, especially near MFD, which means the slightest movement can sometimes cause you to miss focus. This is the same with using any fast prime wide open.
This lens is very sharp wide open and even more so stopped down. A few friends own the 35 Art which I have tried and vice versa with my lens and we find that sharpness is equal. The 35 Art may have the slight edge at f2, although that is because it has been stopped down. So if you were to compare the 35 Art @ f2 and 35 IS at f2.8 which is stopped down one stop for each, you would get equal results. It does have quite heavy vignetting wide open although personally it doesn't bother me. I find that I prefer the image with the vignette rather than removing it through lens corrections. Distortion is minimal and very well controlled considering the focal length.
The bokeh on this lens is very nice and smooth. From what I've seen in other reviews such as The Digital Picture's review, the bokeh on the 35 IS could be considered the best out of its competitors.
I really love this lens and couldn't recommend it more. I don't see how anyone could go wrong with it. It may have had too high of a price at launch, but at its current price it is will worth every cent spent on it. Another point I think most people who own this lens would agree with is, if Canon release a updated 50mm and 85mm just like the 35mm f2 IS, many people (including myself) would be VERY eager to buy them. Below is a few of my images taken with this lens. It may not be a very thorough review, but I hope it is enough to help some people.