I liked it a lot, but not enough to buy one. It's a nice lens - build quality is nice and the range is really great. Image quality is pretty good from what I have seen out of it so far. Out of my kit, 24mm is the widest I have and the widest I have used, so this was pretty wild. I could have shot the exterior photos with my 24-105, I really just needed it for the interior work later in the weekend, but figured I would use it as much as possible. I came back the next day and used it with an on camera bounced flash for some photos with clients in the building and also for some event work later that day. Definitely gives your photos the feeling that you are right in the middle of the action which is cool. It's very easy to get unlevel and get some warping distortion (I mean, that's a given with wide angles).
After reading reviews, my copy was a little softer at f4 than I was expecting. I think I would mostly use a lens like this on a tripod for what I do, so I don't really feel like the IS is necessary for me, but could see where it would come in handy from time to time. I think it's a little too expensive (in my opinion) for what it is. It's not a lens that I would use a lot, but it would be nice to have. I will be looking at adding a wide angle soon, but I think I will save some money and go for a 17-40 f4L instead.