This is one of the best entries I've seen! The puzzles are rewarding once you learn to solve it. Each puzzle teaches you the mechanics that are recur again in the next level but harder. Knowing when to use these techniques is super satisfying for the player when they get it right!
I have but one minor suggestion on the level design. Don't worry, this didn't affect my rating one bit. I think it would be better if the whole level is visible within the screen. It helps players plan and have more foresight of how to solve the problem. I think the restriction of not seeing the entire level doesn't make the game feel better.
Other than that, I appreciate how pressing two opposite directions stops the block on the grid. It's these little things that make the game great! The controls never got annoying. This so far is the best game I plated where the theme was related to the actual controls but was still addicting to move around.