NixOS
Distrowatch started out their review with, "Nix is an interesting distro. The operating system largely acts as a method for showcasing the advanced Nix package manager which offers atomic updates, rollbacks to previous generations of packages, and reproducible builds. This makes running a distribution with Nix as the package manager fairly flexible as well as reliable in the face of package upgrade issues."
Well, "interesting" is what I'm always looking for. The Calamaris installer offers the largest selection of DEs that I've ever seen. I think you will all be impressed. Because I'm most familiar with Plasma, that's what I chose for my experiment.
One thing that few distros I've seen is that Nix will resize itself as I enlarge the VBox window. That means that, as I work with the distro, I can easily make it larger or smaller as needed. Other distros have required going into the system settings and changing the resolution in the Display settings. This wouldn't be much of a feature when Nix is installed on hardware, but it's surely "nice to have" for a VM.
This is just a start, of course. I haven't installed any packages yet, or configured anything. There'll be much more before I'm done evaluating Nix. I'm especially interested in exploring the Nix package manager. It's said to provide access to 80,000 packages! (Maybe that will include my favorite games?)