My M4 is a user. It came to me from a photographer who had used it as a second M-mont body but has switch to digital. This thing is built like a tank. My first impression was how heavy it feels for the size. Real feeling of confidence, not that I'd be able to take good pictures but that I could defend myself with it. 

This one sports a Elmar 50mm f2.8 collapsable lens. First challenge was learning how to extend and collapse the lens. Not that hard and makes for a smaller profile. Not quite a pocket size but streamline to go in and out of bag.

Next challenge was remembering to extend the lens before use. Range finder does not look through the lens like a SLR, so your on your own to make sure the lens is ready. That assumes I remembered to remove the lens cap. Mine has an nice original Leica metal cap so, grateful as I am for the pictures, they are a bit underexposed. Not for want of trying.

Range Finder - I had to learn to focus, not as easy as the FM3a SLR focus, but that was due to me. Also no meter so sunny 16ed it. Overall an intuitive manual camera that once I figured out the lens and focus, it just worked and did the job. Not sure it could say the same of me.

Mine was made in 1966 as one of the first batch of 3,000. 

My Take:

Ok I get it Leica good! No really, I think I get it. The M4 is not the ultimate in the M line but still a nice bit of workmanship. It just feels nice. A bit heavy but I liked it a lot. Not the simplest to use first time but I think it would become more intuitive with practice. But I won't be practicing just now: on to the next camera. 

Lens: Elmar 50mm f2.8

Film: Kodak T-Max 400

Links:

Original Manual for the M4: http://www.butkus.org/chinon/leica/leica_m4/leica_m4.htm

Article on the various Leica Ms and how to pick:  http://www.japancamerahunter.com/2012/11/what-is-the-best-leica-m-for-you/

https://www.cameraquest.com/mguide.htm

Leica M Serial number list:  https://www.cameraquest.com/mtype.htm