Since I moved to Linux as my daily driver, I've been using Darktable as prefered editor. I do have to say that I'm not a high demanding user, so you'll have to take my experience with a grain of salt.
Coming from Lightroom there's a slight learning curve and it's not as refined as Lightroom. But once you get the hang of things, it's really a great editor. Definitely quick but also really usable. The interface can sometimes be somewhat confusing, I can recall several occasions at which I didn't really know how to use a tool or preset. Luckily I'm better at googling than photography. I don't miss Lightroom at all and as of yet have not encountered any missing features.
