I currently use some older Leitz M-series lenses. They're excellent. I'm sure I never use them to their full potential.

I think the "glow" thing is not specific to Leica although I've read that the design philosophy of Leitz was one of the reasons their lenses had a certain look. I have some photos done with old manual focus Nikkors that have that look. A lot of it has to do with the film, developer and printing as much as the lens involved.