Despite the simplistic gameplay and visuals, you've managed to achieve a lot with this one. The levels are really well designed, the mechanics are well thought-out, and overall it's a really fun game. No distractions, no bells & whistles, just pure game design.
That level right before the one with the green door & buttons was pretty neat. And the way you introduce new mechanics is intuitive and pretty well done.
Also: "There is more to be found" at the end really got me. I noticed secondary portals in some of the levels, like in level 3 for example, but I couldn't for the life of me figure out how to get to it. I realise that when you grow to a tiny, tiny size, you can move through walls for a few seconds before the level resets, but I tried over and over and could never make it to the portal :(
DM me a hint? I really want to find out!