First off, the obvious: Despite being a game about a block trying to avoid other blocks, this game is gorgeous. You've really nailed the particle effects and animations and lighting, making this feel incredibly polished.
I also really liked the controls. The player might be a tad too slippery (and maybe a bit too fast?), but the movement feels great, and I particularly liked the implementation of the dash (and that animation is so sweet!). Adding the two coloured blocks with different effects was fantastic, plus the random beam of doom every now and again helped keep things fresh.
However, I did sometimes have moments where the best strategy is to just stand there, not moving, which seems counter to the intent of the game. Perhaps more targeted blocks is a way around that? Also, the alternate you taking over seemed to mostly just do nothing (i.e. just stand there), which means that most of the time, it was fine, except for the few times a block was about to crush me when it happened.
Needing to use the jump button to break out of the control usually caused me to fly into a random direction because of how the jumping works next to a block, but perhaps that was the intent?
Though my biggest complaint is the time it takes to restart! Having to switch to a mouse to click on the restart button was a bit tedious, specifically in a game where my average run was 20 seconds long.
Anyway, an excellent game that feels really nice to play. Fantastic job!