The Nikon FM3A is the only aperture priority camera today that has all shutter speeds available when batteries die. There have been some attempts at this capability - such as the Canon New F-1 and the Pentax LX but these two only had sync to max speed available when batteries expire. I suppose being the only camera with this capability makes it desirable but on top of that it was also a merger of features from two other very successful Nikon cameras - the FM2 and FE2.
Making it an instant classic . . .
For myself, the fact that Nikon had to keep engineers from retiring to achieve this design was what pushed me over the edge . . .
Manual-focusing SLR camera "Nikon FM3A" born in the 21st century
BTW, that pancake 40mm lens shown in the magazine cover - released with the FM3A, is also very desirable and commands a hefty price tag. Kills me when I see Pentaxians complain about the Pentax pancake lens price which is usually available for much less . . .