As for today, I have a lot of games to rate, have to rush and don't have time to test all levels for too long unfortunately. If you're willing to develop this game further, 1). you aren't tied to the theme anymore (though focusing on +/- helps to stand out above other sliding box puzzles a lot), and 2). you really need a proper testing team to tweak and arrange that many levels, with trailing mechaincs and concepts in consequent levels and gradual difficulty increase. Sadly I don't think I'm the best candidate for that, with all my own projects and busyness.
As for my short playthrough, the moment with "-" sign deleting part in the middle, and moment with using L shape to complete a level was "WOW" moments for me, good experience. If I ever find time to play more and have more feedback, I'll let you know. Good luck!