been playing for a few weeks. oddly addictive game, i do agree that an additional layer of interaction would really bring it to the next level. (i.e. some form of upgradable items, or cost reduction items, or chances to fight "boss" blood cells, etc..). before trying to add a ton of things, it may be helpful to update the blue background also, small visual changes can add freshness to what the player is seeing. i like where this is going, and look forward to seeing more.
..........although....... there is one problem...... i logged in today and clicked on "new game" instead of continue, and the game auto-saved instantly now... sooooo, time to start this new game!