I feel like Nix does have such killer features, but they are different for everyone.
For me it was:
- system management (nixos + nix-darwin. I wish there was something like nix-darwin for non-nixos linux distros, binding daemon systemd units and desktop files into the "hosting" distro)
- on-the-spot running without globally installing for one shot tasks (nix-shell -p iotop --run iotop)
- "just works" project environment (default.nix+shell.nix or flakes)
These are the ones that made me tip over and decide to go from tiptoeing to full tilt