This game
totally needs to be made. Without even knowing your story, which sounds wildly imaginative in its own right, the gameworld itself would become an integral element that's just bursting with possibility. The human body from within? Oh man, the potential is staggering in the right hands (and by "right", of course I mean "yours").
And you're certainly correct that Osmosis Jones was a giant turd. Even Chris Rock couldn't save it.