Unplayable.
Good idea, but it just didn't get through here. Cells constantly going off screen, the small screen size, the sudden storms of white blood cells and antibiotics (especially when you've only got once cell infected and all your other viruses are dead) are huge issues, and the worst one is the fact that for some reason, it almost NEVER picks up the virus that I clicked on. I'm not even kidding. I'll be trying to rescue one going off screen, only to click on one nearby that's going in the opposite direction. And guess which one the tip of the pointer was on? It wasn't on the one moving away from that edge, I'll tell you that.
I like your games, but I simply cannot play this one. At the very least, if you cannot or will not fix these problems, add a Level Select option so we can grind to upgrade, and thus survive the impossible levels.