The only reason I like Nikon FM is that it's capable of taking non-Ai lenses, which could really benefit Nikon users, and I am one of them.
Many of the non-Ai lenses are well designed and inexpensive these days. And the total price you pay for stays relatively low, so it's really practical.
Also, if you compare the size of the FM body with a small lens like the old Auto Nikkor H 50mm F2, attached to it, it's not that much bigger than a rangefinder camera with a normal lens.
The shutter sound on the FM is pretty loud and ugly, but that's about all the problems I think there are. So, this is the camera I alway go back to.