First off, tThe idea of the game is very instinctive, adding and subtracting is very easy to do especially since you only need to add 1 and subtract 3, and the game mechanics are mostly 3 ( collect black orb, collect white orb, touch dark wall ), therefore, in order to make your game interesting, you'd have to whip out new kinds of challenges and game mechanics the more the player progresses through your game, in order to keep them playing and get better reviews.
For example, you could give the player the ability to open doors if and only if his darkness level is 0
or, you could give the player the ability to destroy a specific kind of wall if his darkness level is 3
the sky's the limit here, the more mechanics you add ( as long as they're not overwhelming together ) the more the player has to think.
Secondly, for the love of whatever you believe in, make an undo button. It would only save on the player time and effort, and puzzle games should not make you suffer.