It seemed to me that the difficulty increased very quickly. And when the stones came super fast, there was not a lot i could control anymore, it seemed like it was impossible... Maybe some more balancing? Otherwise a nice game!

Good

As i commented, the most important feature, the gameplay, is really good! If you felt improving this game further, you could maybe improve design and sound, or maybe offering additional color / sound schemes

I like it a lot, but since you asked for feedback:

I would make the switch block and flip block movement more responsive, different sounds or something, maybe some small animation even. After a while i just hit whatever key and hope to end up with one that works. :D Maybe thats just me... maybe you could start with a smaller selection of less complicated cubes to give the player the possibility to warm up. (Fun first, challenge later) Its more fun to understand the game mechanics by yourself without too much pressure i believe.

Oh, and please remove the PAUSE OPTION FROM THE ARROW UP KEY, you evil genius! I paused 20 times and felt like a dummy :D Just kidding, but yeah, i would move that, since most tetris player expect a rotate. I don't remember if there was a setting for volume of music and sfx, if not, having one would be nice! Cheers!