My Sparta strat: Towers (from top to bottom) Max missile launcher, max fan, max quake box, then buy a grenade launcher (upgrade however you'd like with remaining funds). Enemies should never even touch the wall.
This game, while amusing, was clearly not a victim of extensive playtesting. It's also ironic that the game mode "Realistic" is anything but (world-wide panic over a disease with no symptoms and no efficient vectors, for example). The author of the game has made it clear that he doesn't care about any issues relating to the game, in fact, his response to feedback was "it's a flash game, live with it. No ones forcing you to play it if you don't like it.". It's amusing, but in the end, it's a great idea with poor execution.
 "Earth Defense"){kind=icon}
 "Storm the House 3"){kind=icon}
 "Pandemic 2"){kind=icon}