I have the 3.6-18 Mk5. So far, I like the capped windage & locking elevation. I like the adjustments on the elevation (nice clean 'clicks'). I only have about 100 rounds with the scope so far this year (on an magnum), so it's a relatively small sample. But I've yet to have any tracking or RTZ errors...time will tell.
The parallax is finicky compared to some other scopes I have (to be expected), and adjusting the dipoter on this scope took longer than any other optic I've owned. The optic seems very bright to my eyes. I'm not an expert, but I think this may have to do with the coatings. If so, we'll see how the coatings stand the test of time. I think the field of view is OK, I'd like more, but I think it's competitive.
I don't like that Leupold charges ~$400 extra for illumination. But I like the integrated throw lever & the factory lens caps work just fine. I also don't like the 35mm main tube. I would like to run this scope on a hunting rifle with integrated ring/bases for weight savings and so line-of-sight is closer to bore, but I'm currently stuck with a pic rail.
I picked-up my non-illuminated Mk5 for $1,400, and I think it competes well in that price range. It's not an end-all be-all scope for me, but I'm not looking to sell either.