I got stuck on level 9, mostly because of the 3D "illusions".
Gameplay
Pretty much perfect, good UI, well explained gameplay, very interesting puzzles and mechanics. It took a bit of time to get used to left/right hand controls especially when the characters are on the right/left sides, maybe switch them up so they're always on the "right" side?
Graphics
Art is really good, but I faced one major issue with the graphics: it's often impossible to determine if something is actually in front of something! I got stuck on level 9, mostly because often I ended up falling into the void where I thought I would just go down one block. Making the camera movable with the mouse might help, but I think you need to think the design better, maybe with shades of blocks depending on the layer. I'd be happy to give feedback on a future update!
Audio
Perfect. Great soundtrack, unexpected but highly appreciated voiceover in the intro, and just the right about of sound feedback on actions. If I had to nitpick on one thing it'd be the button hover sound, slightly too "strong", but really everything about the game's atmosphere is perfect.
Innovation
Again, perfect. This is a great single player game that accidentally doubles as a sweet co-op game, with very interesting mechanics and constraints and the idea of falling into the other's arms is adorable.
Theme interpretation
3 stars because I couldn't find a link to the theme, but I feel like there's one, somehow.