Nice game with an interesting mix of physics puzzles/platforming/exploration. I got stuck on the last level when I got to the stealth bit, had no idea how to get past those guys to get up the slope, except for shifting metric tonnes of rock up all those platforms and I didn't want to do that :/
The music and graphics and the whole way the game was put together (menus, level transitions etc) was very solid. The graphics and UI communicated everything clearly, and the objectives updating in the top left was nice.
The one thing I think would improve it most would be making switching masks quicker, maybe putting them on keys 1,2,3,4. So many times in levels 3-6 I only cared about strength + beast mask, but always having to cycle through the other masks, waiting for each animation, took a few seconds and seemed like unnecessary friction.
Overall I'm super impressed with how much you managed to do, I think it's a really cool game. xD