Summary: I compared this lens to a Sigma 30mm F1.4, the Canon 24mm was softer at the same f2.8 stop on both lenses. Neither lens is a great lens with the sun in frame, which I expected with the Sigma, since it is designed for speed. The Canon 24mm is not that fast of a lens at f2.8, so I thought I would use it as a sunset lens. The lens makes a horrible triangle shaped flare, along with other rainbow patterns. The lens also did poorly with shooting a skyline at night.
Summary: I bought this lens to widen the views possible on my EOS 10D. The build quality is great. It feels like a little tank compared to the 50mm f/1.8. It's only sliiightly larger but nicely heavier than that lens. But, check the weaknesses.... However, AF and overexposure issues make this lens untrustworthy for anything that isn't a throw-away snapshot or bracketed in underexposures.
Pros: Depth of field is great. The horribly wrong autofocusing is quick, and f/2.8 ain't bad either. Build quality is great. It feels like you could throw it at someone, hurt them, and pick it up and use it again.
Cons: Here's the main problem: It brutally overexposes everything on my 10D. It's not reliably "x stops off" of you would simply set some exposure compensation whenever you mount it on your camera. It's very hit and miss. I've had some great shots with it and about 75% horribly, uncorrectably wrong shots with it on the 10D, even in RAW. On my ancient film Rebel it seemed OK on 4x6 but that doesn't satisfy most of us pixel-peepers. It's also the worst AF on my 10D of any len...