Sigma's website claims this lens 'cannot be bad, because it is the latest lens,' well, that's an odd way to put it, but they were right, at least in this case!
The Sigma 30mm F/1.4 DC DN is a fast 'normal' lens for your APS-C and micro four thirds cameras. It's slightly on the wide side of 'normal' for APS-C users, about 45mm in 135 film format, and on the long side for MFT users, with an 'equivalent' focal length of 60mm in 135 (full frame) format.
The technical image quality is very high; F/1.4 is totally usable even for landscape photography in low light, and there is no noticeable coma in the far corners! Other positives include low axial color fringing, (but not lateral), and a simple distortion pattern which is easy to correct in post processing when shooting RAW. I should also mention the very reasonable price, especially for this kind of performance.
There are a couple of negatives for pixel peepers...