Leitz was clever about the way they designed this lens. They made it so the aberrations show up mostly in front of the plane of focus. What this means is that if you take a photo with lots of OOF foreground in the corners you will see nasty corner swirl/bluriness from f1.4 diminishing until about f2.8. But most people don't compose this way, or else the corners are too dark to show the coma. I looked at hundreds(ed.:well, I didn't count but it was a lot) of photos taken with it on flickr and could only find a few with OOF foreground that showed the effect. Most people put the subject in the foreground, so the background is OOF. At f2 the lens is noticeably better. I wish I had a first gen Summicron to compare it to, I bet it's similar. It's low contrast wide open, but it actually controls veiling flare really well (compared to an uncoated tessar type lens, for example, which can not be pointed toward any light source without washing out the picture). What you'll see is flare around edges and "glow" off of light surfaces. The depth of field is very shallow at f1.4, which may contribute to its reputation for softness.
At f4-f8 I think it is a superb lens, and that's really the main reason to own it. I find I only use f1.4 under really dim conditions, where the character of the lens seems to match the character of the light.
