Overall I'd say the puzzles were not too hard but did take a little thinking for the later levels, the graphic were nice and the music was very cool.
I ran into a glitch in a level with portals (I think it was level 22): I used Undo a few times to backtrack and then realized a few backtracks wouldn't be enough so I tried to reset the level, but the level ended up not completely resetting to its true initial state (something more like how it was when I went through the last portal), and after continuing to try to futz with it I just ended up in a completely softlocked state where neither the undo or reset buttons were getting the level to a playable position anymore. Fortunately reloading the page let me continue at the same level and finish it.