This is a great puzzle game! Definitely reminiscent of Portal. It really makes you think, right from the first level! The level design is great as well, especially when you have to use portals from previous levels! Really adds a feeling of continuity to the game.
I think the 1st level would have been better as a later level though. Focusing more on the mechanic of portals first before its various applications would have been better build-up.
Also, I think the player accelerated during its run too fast? Or at least its horizontal velocity is clamped too high or not at all. I feel a slower movement speed would allow tighter movement and would make the player focus on portal movement.
Overall a great game!