Stamped

I'll say right off the bat, the in-game instruction is already better than nearly every jam game I see. The "Hold A/D to rotate your shape" and "this way" arrow are much more intuitive than having to read a wall of text. It could still be better though. A simple graphic showing the WASD keys with A and D blinking will tell the players what to push, they can observe themsevles that it rotates the shape, and an arrow appearing after a few moments will let them experiment for a couple moments. 

Noticed the same on the following rooms. The tutorial was better than most, but could still be more concise.

The jump cooldown is a bit tedious, and I'm wondering if it could have been shorter or eliminated entirely.

Holding F and R to clear the shapes is also pretty tedious, I'm not sure why a quick push of the button wouldn't have sufficed.

The jumping mechanics could uses some polish. Horizontal movement in-air is too floaty.

The first place with the killbox was a bit too frustrating and where I decided to give up. I completely found out on accident that you could rotate the stamps with scroll wheel. A simple mistake sending me back to the beginning of the room was too punitive and I didn't really have motivation to go over the wall just to fall into the killbox again. I think you were trying too many mechanics at once. First teach them to build a bridge over a killbox. Then teach them that ramps will make them fall. THEN teach them that a ramp can force them into a killbox.Then have the long climb in a different room so theres no chance of failure putting them into the killbox they already passed.

Last thing I'll say is that having platformer controls for movement and mouse controls for stamp placement isn't good for a focused game experience. I feel like I'm playing both parts of a 2-player game, or two games with wildly different mechanics.