A neat idea, I like that it even gives the people names as you go through their organs, a nice touch.
I realized after a short while though that I could just hold down space and the organ would die before anything could reach me, I think just increasing the organs health bars would solve this so you have to make decisions based on fighting/dodging/eating.
If you had some textured backgrounds to represent each organ it will help with the feeling of moving around.
Other than that I also liked the sprite art for the bacteria and anti bodies.