Ooh I like this. The sound, the graphics, the puzzles. This is really tight.
The quality of the tutorial alone is really impressive. Very high standard of quality on your explanation of the mechanics, and interactive learning.
The concept of using yourself as a wall is, probably, not a novel one, but here it is executed perfectly, and definitely feels novel to me. The restart button is super juicy and adds to the game a lot. I like that you can queue button presses while the growth animation occurs. When you return to existing levels with portals, and the solution is somehow simpler and also harder, that was a really awesome moment.
As for critical feedback: I find the growth speed to be a bit too slow. If it were really really fast, that would feel bad, but maybe if it started slow, but ultimately completed it's motion faster, that might be a nice trick. A little less time spent idling would really improve the gameplay loop. One of the levels was arbitrarily easy, but suggests to collect stars. A better design would make it *somewhat* easy to solve: I don't think any levels should be arbitrarily easy because that sort of dissuades the type of player who doesn't collect optional achievements. The following level is of course extremely easy, but as it is there to introduce a new concept, that's of course great! I'm also not a fan of the levels that give you 50% chances to succeed or fail.
You seem to have a knack for this genre. Keep it up. Some clever design here.
I'm very glad you liked my idea! Player speed has been on my mind as well. I will definitely consider to speed that up a notch. Your comments on the level design are really insightful as well. I had not considered that some players will (of course) not care about the collectables at all. Thanks for the encouragement :)