Addicting
Played 5 minutes so far and I'm pretty sure I'm hooked on to it.
Originality - Taken some good ideas from other games and combined it. The result is awesome
Audio - I personally like the music and its suiting for this game as well. Sound effects are a given for any game.
Side-notes - The game definitely has room for improvement. So far, I think a toggle for health bars to show would be a nice addition. And for unit selection, perhaps a numbering system to either summon zombies or to select different type of zombies. Overall, a key-map would be nice. All of the improvements above are just for convenience though, the problems, if you can call it that, doesn't really affect the game negatively.
9 because its a great game, but its not perfect, yet.