I have an FM2, I bought a Leica M4 a few years back. I still have the FM2. This is what I wrote about my M4 experience a while ago:
Originally Posted by rakeshmravi
I will also say in retrospect that I didn't like the arcane film loading, I hated the cost of the lenses, external viewfinders for ultra-wides is a huge hassle and the body was the same size and weight as my FM2. The small lenses are great - the cost not so. There was nothing that I found the Leica could do that the Nikon couldn't (except bleed my bank account dry), however, the Nikon has depth of field preview, fisheye lenses, easy film loading and can focus close.
Originally Posted by perkeleellinen