For the money, this is a pretty decent lens. It's big (roughly the same as my 28-70L), but very light. Build quality seems pretty decent for the money. AF motor is a little loud, but the sound isn't as annoying as a Canon non-USM motor. I don't actually mind it at all. Focus is fast enough...I'm not shooting a basketball game with it. IQ seems decent, although I haven't had a chance to really run it yet. For the money, I think it's a bargain. No, it's not an L lens but you're not paying for one either :0. The only gripe I have so far is the goofy hood/cap/ring deal...I couldn't care less if the hood is built in (I always use one anyway), but having it vignet with "adapter ring thing" on is a little annoying. Oh well...that's what you get at 15mm on a full frame camera I guess. And did I mention that 15mm is insanely wide on FF? Distortion seems like it's about what I would expect on a rectilinear lens this wide.
If you're looking for an ultra wide, this is a good choice for the money.