Great Idea!
Its a fun game from what I played, reminds me of a missile defense game, defending a grounded target, except your not shooting anything. Yet so very different.
I like the idea, your a parasitic organism, feeding off of the hosts blood cells, before they reach a certain point, what point would that be?
The music fit very well, as if the music describes a parasite, and what its doing the host's body, as if the host will eventually eat so many blood cells to the point of the host getting sick from lack of immunities and eventually dying out. and also the music is fitting, a good theme to be deep inside a body causing havoc. It reminds me of that game here on NG as well, pandemic, your a virus, trying to get the whole world sick through smart tactics, trying to get every single country infected, before some countries get smart, and either block off their water sources, boats or airplanes coming from the infected countries. Get any ideas from that game by any chance? I'm in no way saying that you stole an idea, just curious.
I liked the upgrade system, I'm sure it proves very useful later on, keeps the game interesting, a shame without it.
Good controls and graphics as well, the controls were smooth and easy to get used to, and the graphics were of high quality, can't have a decent defense type game without this.
A few suggestions, make the background look like the innards of a body, instead of black nothingness, maybe some skin cells, a few veins, entrails, maybe an organ or two, to look like your drifting inside of an actual body, and on cell lanes and tubes below your current position, maybe show some traffic of red and white blood cells, zipping throughout the trails and cell highways of the body. And instead of exploding, actually show the parasite consume the blood cell, but in a quick process enough to keep up with the pace of this game. One more suggestion, make the parasite you control look nasty and grotesque, to be truly name worth of a parasite!
The game is good the way it is, just a few minor suggestions, yeah sorry I get in a rant.
Overall enjoyable, and for sure I'll play again and acquire many upgrades.
9/10 Stars.
5/5 Vote Panel.
xVegetAx, NG Portal Lieutenant.