While I liked the portal switching, sometimes the portals were out of reach, making progress impossible.
The “unreal” side isn't really unreal, it can still kill you, and it's basically the same as the “real side” except for the floating bullets (at least I couldn't find a difference).
The music choice is really nice tho, even though it's a bit distorted in the “real” side, which is confusing considering the fact that it's “real”.
I liked the power ups, although I hoped they would save me from falling, since it's really the biggest threat in the game.