Really fun! I will steal this!

No bug, but the level was escalating too quickly.

Oh yeah I forgot to tell you that I only reached level 5

I find out that brown cells are very though. Plus I can't spam (click hold).

Great time waster.
I really like the game and the upgrade system motivates.

All in all great game. =)

Nicely done, a very original and advanced shooter, with all these upgrades.

I regret there is no indication of the current level - the player has to count them and remember the current one.

I was confused during my first game session, as I seemed unable to do anything. I recommand you to change your instructions this way : "Place the mouse pointer on the left of the dashed line and click the left mouse button to release your white cells and fight the bacterias.", instead of "Click and hold left mouse button before the dashed line to release your white cells and fight the bacterias."

Ideally, you may make disappear the mouse pointer from your screen applet and replace it by a forbidding red "X" sprite on the right of the dashed line, and a white "O" sprite ( a hollowed white cell ) on the left of it.

Nice style, I love the wavy background. The game is also quite cool, with a nice fit of "story", graphics, and gameplay mechanics.