i've had a hexar rf for two years. i tried a 35/2 asph once, it focused fine. my 50/1.4 nikkor ltm focuses fine, too. it's probably best to avoid low serial numbers. i estimate that #1445xxx is a good cutoff mark.
build quality is the same as the leica mp/m7. titanium covers over aluminum chassis. same weight. even the frameline preview lever and shutter speed dial feel the same. you can easily turn the shutter speed dial with your eye to the viewfinder because it's in the rear corner. the shutter button is easier to gently release, with no need for softies. very precise response and positive feedback. easiest film loading available. along with the minolta cle, it is the only modern m-mount camera with a self-timer. the softcase is also the best one ever made for an m-mount camera.
some people gripe about the motor wind, but it hasn't been a problem for me. leicas aren't quiet enough to make a difference when it counts. only a hexar af or other leaf shutter camera can do the job right. the shutter sounds very different compared to the single bladed zeiss ikon and double bladed voigtlander r3a. it's not metallic or loud, but dull, short, and quieter than a well used m3, even. the weight of the body must dampen the volume compared to the zeiss ikon. i have high hopes that the digital m8 will be the quietest leica ever, by a hair.
i wear glasses so the .6x viewfinder is perfect to use 28mm and 35mm lenses. i'd like a .72x body for 50mm lenses and to not have to switch lenses, though it's not a must have. the multicoated viewfinder is brighter than any m3/m2/m4/m5 i've ever seen, but the m6/mp/m7 are brighter. the m6 sacrificed a condensor to achieve its brightness, making it flare easier, but the mp/m7 have multicoated viewfinders so they put the condensor back in.
tom abrahamsson says the hexar rf is notorious for its meter display disappearing in bright sunlight, but it's never happened to me. *shrug*
that said, i think i'll eventually get a .72 m7 for a second body. i like the occult rituals associated with the leica m.