Excellent game.
Great example of a well-executed RTS/defense hybrid. The concept is a great one though the game itself could've used a helluva lot of polishing up.
Things to point out:
+Great idea.
+Good difficulty - if you play your men right, zombies fall like flies; time the simplest of things wrong and you're fighting a losing battle...
+Plain fun.
-Outdated visuals.
-Crude interface.
-Grammatical mistakes here and there.
-Zombies advance too close to not-retreating squads while chasing after retreating ones, it's illogical.
-Final level offers no challenge (Obliterator Squad).
All-in-all a kickass game which definitely deserves a sequel. And if you do get around to a sequel, ADD A CRAPLOAD OF UPGRADES FOR EVERY CONCEIVABLE THING. People love to upgrade things >.>