Man, I am racking my brain trying to think if this concept has been done before, but I can't think of anything. It reminds me of some of the ice levels in Chip's Challenge, but Chip wasn't a snake.
Excellent work on this. Controls are smooth, puzzle concepts are introduced gradually, graphics look really clean, and progress saves. Feels like a forgotten classic.
My one and only complaint is that the titles of the levels stay on screen a little long.