The vignetting (distortion at the edges) is pronounced, but can be good with Lightroom 4/5 correct. The lens is also visible chromatic aberration, but may correct the EOS M itself automatically good without which one would need Lightroom. That the lens has a very high build quality has already been mentioned. Positive you can still mention the image stabilizer allows good pictures without foothold to make.
I highly recommend this lens mainly as a kit lens which is almost given away in the camera (all under 300). Another very good landscape lens is the 11-22 mm which has a larger viewing angle. This will probably be the next purchase.
btw. I just use the RAW format and Scan mesitens in M mode, so I can not say much about the JPG corrections for lens
