Speaking for myself, I would make these changes to make the controls smoother:
- Add some sort of animation and sound effect for holding down the space bar to build the mental connection between the space bar and the grow ability.
- Make one tile tall cats be closer to actually looking like they're one tile tall. (Their sprite is more like 1.6 tiles tall, which makes it hard to them distinguish from 2 tile cats.)
- On levels with blocks falling from a high area, include some sort of background object that makes it easy to line up the top of the ledge with the place where the block will fall.