I pretty much second everything already said here, pro and con. Some additional thoughts:
I like the look of the photographs I take with my Z6, especially with the Jupiter 8 or 12 and traditional BW films. I think I can perceive a difference from the look I get with more modern stuff, and it's a difference I like.
In terms of reliability and ruggedness, a good Z6 may be as good as anything out there, thanks to its overbuilt, bare-bones simplicity. In terms of ergonomics and features: eh.
Mine had very stiff wind action and shutter release at first. Over time, things began to loosen up. Now, after about nine months of intermittent use and excercise, both mechanisms are... well, less stiff. I don't need the soft-release any more. Winding is smoother, but some films are easier to advance than others (my bulk-rolled Tri-X being the most difficult), so maybe I have a pressure plate problem.
The stroke is long, so I learned to double-pump. This also eliminated occasional capping, so apparently that 'problem' was due to incomplete winding/cocking (user error!). That thin, toothy wind lever is not what I'd call a pleasure to use, though.
The diopter lever is easy to knock out of adjustment. You may have to fiddle with it often.
The door: I've never had it open accidentally, but then I like to keep the bottom half of the leather case on (I cut the case in half). This gives me a comfortable grip and also makes it impossible for the door to open; the downside is that it makes it impossible for the door to open.
With the older LTM cameras you're not supposed to change shutter speed before cocking the shutter. The Z6 doesn't mind. The Zorki feels a bit clunkier to me than a Fed2, but it is also faster and easier to shoot. The shutter speeds are limiting, but I would not trade any simplicity or ruggedness to have more.
The Z6 gave me a lot of what I wanted and needed: a cheap, simple, rugged and fuss-free entree to LTM rangefinders, FSU cameras and old-school film photography. Its flaws and limitations are quite acceptable for those roles, IMO.