fun stuff. when possible, i'd aim to fix up some things.
mainly: music/effect volume, include a menu option as well
mouser sensitivity is insanely high by default, X/Y options are also annoying to deal with. add a "both" slider perhaps, and also tweak the minimum/maximum amount since if it's stupid high by default, i can't imagine anyone ever setting it higher.
there's also some issues like the box on level 2 being able to clip through the walls and so on
if you're stuck on not knowing what puzzles to add, i recommend adding basic option features and cleaning up the UI a bunch, and i think puzzles will occur to you naturally from simply working on the game
keep up the good work