Clearing a room and having everything appear was very satisfying. At first I didn't like that you had to go re-collect the gems, but eventually I appreciated it, as it made me go see the whole fully-filled-in space.
Dashing while pressing multiple directions at once (hard to do accidentally on a keyboard, hard to avoid on a controller, or mine at least) causes you to dash off an unpredictable distance in an unpredictable direction. Usually it would go very far in the expected diagonal, but sometimes a short distance in almost the opposite direction. I had to switch to the keyboard because I kept dashing into walls I wasn't even looking at. For such a grid-based game with narrow one-grid-cell pathways, you might want to consider aligning the player movement to the grid.
A fun time overall