You can install the same desktop environment so that they look identical. The biggest difference is in the philosophy behind how you make any changes to your system. In NixOS, you don't find some random SO post, edit /etc/whatever.conf, then forget wtf you did a few months later. Everything* goes through editing /etc/nixos/configuration.nix. You then apply those changes, and roll them back if you don't like them.

• Not actually everything, yet. You can install most any gnome plugin through that file, but you can't set any configuration options through there yet afaik

I've been on Ubuntu since I first got their CDs in the mail. Sadly, they're determined to snatch defeat from the jaws of victory, and I'm now moved over completely to NixOS. It's like what they're trying to do with snaps, but competently executed.