Super fun! I loved how each weapon had a different play style, and that you had to swap back and forth between weapons to unlock different parts of the map.
Difficulty was at a good level for me. I think it would be helpful to have a very small "mini-map" to show what room you're in, in relation to the game world. That way you can retrace your steps to find old weapons more easily, but it wasn't too hard without a map.