A few years ago I've tried a couple of alternatives, and Lightroom was by far the easiest to use.
If the audience is casual editing (ie. a short time to improve a photo, and little user skills), I think Lightroom is significantly ahead of the competition - in particular, UX has never been a strong point of open source software.
I don't know if the latest years changed the landscape, but I suppose not - Adobe kept enhancing Lightroom.
License wise... that's definitely another story (I personally preferred when a license was valid for a single major version).
Sadly those mentioned open source products are still light years away from what Lightroom can offer.
It is like comparing Gimp to Photoshop. Yes, they can do some of it, but they can't do it better or even close to that if you are serious at what you do.
I am a developer, I have been Linux user for years and photography is my hobby. I periodically try some Lightroom "alternatives" in hopes of finding something good, but they are still nowhere near of replacing it. And with the limited budget they will probably never be as good.
I know only one great open source software example in the arts field, and that software is Blender. Blender can probably do it because they have been receiving millions in donations from major game development companies in the recent years. Unless something similar happens in the field of photography, I don't think we'll be able to get away from proprietary software soon.
Honestly darktable is more than a replacement for Lightroom for me. However I never liked Lightroom in the first place; Aperture was far superior for my use-case. But I am very comfortable editing photos and I don't go to extremes with editing, and I don't need anything more than what Aperture offered 10 years ago.
Blender looks great but is a bit oddball too (though less so now). I’d also nominate QGIS as a good open-source app (UI). Maybe not “art,” but I think it’s become almost de facto for what a hobbyist will reach for first, and it’s generally quite user-friendly. But they are rare!
More than the interface (which is a matter of taste; I prefer single-window), I refer to the experience as a whole.
I've used only Lightroom (as Adobe product), and it's hard to define what casual editing is, but the basic enhancement functionalities were easy to use, and especially, they were very effective (again, for a casual user).
It had, as far as I remember, very good automatic enhancement, that one could use as a base. The other products I tried weren't so effective. If, as I suppose, this type of functionality requires a significant investment to develop, then it's out of reach for non-very-well-funded open source development.
Dehazing was another typical example of LR functionality: it's stupid simple (a slider), and does effectively what's supposed to do for a casual user.
If the audience is casual editing (ie. a short time to improve a photo, and little user skills), I think Lightroom is significantly ahead of the competition - in particular, UX has never been a strong point of open source software.
I don't know if the latest years changed the landscape, but I suppose not - Adobe kept enhancing Lightroom.
License wise... that's definitely another story (I personally preferred when a license was valid for a single major version).