Before I can take Neovim seriously, I need a Neovim GUI that is exactly what gvim or MacVim provide — not something that adds features I neither want nor need nor can I easily disable.
Granted, it’s been about six months since I’ve used VimR, but I bounce off it every time, because it doesn’t work with the configuration that I have built up trying to match my Vim configuration to the best of my ability.
Having used MacVim for several years and now using Neovim mostly in the terminal but sometimes VimR, I disagree that it's a mess.
I get wanting to have a common gvim ui/ux across platforms, but I think having a Mac-like or Windows-like ui/ux on those platforms mostly trumps that.
Also, the special features of VimR, like the built-in file browser and Markdown preview can easily be disabled. Using the native rendering of macOS and support for ligatures, for example, is certainly a plus IMHO.
VimR is very good; I've been using it before it started using Neovim as the core [1].
[1]: https://github.com/qvacua/vimr