Nice!
You definitely need to make it endless, don't increase difficulty and then add some sort of progression. Some tense parts needing pixel hunting are a bit off or just need extended margins.
This can be game for hours to play. Digital popit/spinner/simple-dimple.
As a puzzle - it progresses a bit slow, first dozens of levels are too easy. Also there is no progression, at least level number to grow - can't even say where I'm done.


