Good game
Ok, here it goes XD:
The main music was completely awesome, ambiental music was the best you could use for a game like this, the bad thing, was that as soon as the level started, it faded completely and it was left with an atmospheric sound... It would've been great if the whole level had the same rhythm as the first ten seconds.
This game kind of remembered me Grey-Matter, which also was in the top of NG like a month ago or so. It's a simple, yet effective game. I found the controls a little bit heavy, perhaps you could make dissapear the cursor of the mouse, or add an option to hide it.
Also, if you hit a wall, the whole screen bounces. Perhaps it would be better only to add a limit function boundarie to prevent to screen from bouncing.
Lastly, variety is the best thing in a game. You can keep it simple, but it would've been great to have other type of blood cells, maybe with different sizes or shapes.
Other than those things, great game. I enjoyed it.