I have had the Sigma 30 1.4 for a 3 years now.
No focusing issues with my copy. Sharp wide open, great color etc.
Took thousands of pics with it. It focuses very well, also under dim light,
looking back at oof pics mostly were due to user error: the DOF at 1.4 is very thin and the camera can decide to lock on say, the corner of the nose just because it had a bit more contrast and render an eye blurry, just an example. It happens with other lenses as well, but it is more pronounced at f1.4.
I recently took it outside, stopped down to f7 it is amazingly sharp, so it could be pretty good for landscape if you don't mind the angle. On FF, i am not sure i would use the 35mm much, and if i go FF i'd probably get a 50mm 1.4 to replace the sigma.
Focusing is pretty fast, not like my 17-40L, but it has a lot of glass that has to be moved and stopped accurately, I didn't test the 35L so I can't comment how they fair in comparison first hand, but Lightrules' reviews go a long way in my book. I think the EF50mm 1.4 focused faster, but it is smaller lighter lens with less glass to move around.
The build quality is nice and the finish is pretty good. L lenses are more rugged and have (usually) weather sealing. My experience with Sigma is that they are not very rugged so if you make your money of it, just invest in a sturdier tool regardless the what seems to be marginal IQ differences.