Cool concept! It just needs a bit of polish!
The puzzle concept is very cool, its a basic block pusher with a directional twist. However, it was a very rough ride figuring out what the puzzle mechanic is.
I'd like to start by addressing the art, as I feel it was my first barrier to learning how the game functions. When the first level started up, I took one look at the screen and had NO idea what was going on. I didn't know if I had a character or if he was on screen. I couldn't tell what was space and what was a wall, and I didn't know what the movable block was. The art style you were aiming for is cool. After pushing buttons and starting to figure things out, I realized what you were going for and I think it is cool, but over simplified. There is room for improvement if you can get your art to teach the player just by looking at it. If you can use things like color, shapes, lighting, shading, etc. to teach the player what their character is, and what the objects mean, and where the goal is just by looking at the art, you've saved them a lot of time and helped them get to the awesome part: playing the game!
In terms of level design, each of the puzzles was great. It slowly got more difficult, requiring the player to think slightly outside the bounds of what they did before. But, I do have issues with the first level. After being confused by the art, I had to press buttons and learn things the hard way. I figured out quickly that I seem to control the green thing. I moved my green thing (presumably a dude) over to the pinkish, greyish thing, which upon first inspection, looked like a dude with a mustache. (the black "arrow" was a little misleading at first) I tried to push it sideways, but it looked like I glitched the game and that the thing moved diagonally instead of straight. (I understand this is supposed to happen, but as a new player, I couldn't understand why) Needless to say, I had to fiddle with it for several minutes before understanding the concept, why the block moves two spaces sometimes, why it moves diagonally other times, etc. My suggestion is to add even more introductory levels that have basic blocks. (without arrows) If the player first grabs onto the idea of moving a block, they will have a stronger foothold when figuring out the directional blocks. Even if you seldom or never return to basic blocks, starting with them is well worth it!
In terms of sound design, there isn't much to say. :/ I wish there was some ambient puzzle solving music in the background. If you're willing to put in the work, you could have some sort of series of quick notes when the player moves a block, (maybe C E G played very quickly, etc.) then have it play twice on the directional blocks that move more than one space. This could help the player learn that it essentially moved twice. Even more, you could have the rewind function play the notes in reverse to indicate a backwards movement through time. That would be cool! :) Feel free to use all these ideas.
All in all, it seems like you enjoyed making this! I enjoyed playing it! I think you have a sharp mind for design! Keep up the great work, never stop learning and implementing new things! I look forward to what you come up with next! :)