Very challenging game, I found myself stuck on 509, I think I know what to do I'm just having trouble doing it. I found that once i go through a level it seems surprisingly easy to go through it again, so a level select or something would be nice but doesn't seem like much of a problem if you can build some decent muscle memory.
Top marks for being difficult yet playable, and having a lot of fun interesting uses for the very simple yet solid game mechanics.
Not so much for the limited graphics and lack of save features.
Now about the story, it is just an excuse plot, which is fine because the game is focusing on the mechanics. but it is worth noting that that is an area that could use work, but with a game like this it should probably be the last thing you work on or something worked on along side the graphics.
overall a very enjoyable game, keep up the good work.