A really simple but fun concept, well done.
The speed of the circle that spins around celly is just perfect to keep the player always engaged and that's why this game is so good: it's not too slow (in that case the game would be boring) and not too fast (in that case it would be too difficult). Also, the camera that zooms out when you pick up the food is a nice touch.
I really don't have any complain about this game, the only thing is I'd suggest you is to make more clear to the player that the circle that is spinning is the direction where celly goes if the player presses the button (maybe replace it with an " arrow-shaped" cell or something like that).
Limitation breeds creativity. That is so true.