disfromage covers it well. I use an M4, and have owned M2, IIIf, and IIIC. The early Leicas are very compact, but not as practical to use as the M series. The later models with a built-in meter are convenient, but meters are a potential source of problems. A greatly underestimated lens in M mount is the old Elmar 50mm f/2.8. It was one of the sharpest lenses I ever tested. Also, it makes the Leica a genuine pocket camera.