Not bad should add to the number needed is par and more is bonus have a scoreing system. Have the smiles cheer or somthing the odd sound you get when one goes to home drove me nuts after the first lvl.
Should have a stat pannel for towers range dps effects ext. and should give upgraded towers different looks so you get more satisfaction from upgrading them maybe even a tower and building tree to keep game interesting.
3 out of 5 for a good game base. To make it better maybe add short story to start. add more weapons. increase playing field size. Add more zombies say a ranged one or a a exploding one. among other things.
They REALY need to make it so you can get behind your comand buttons enemy mortar behind one can really mess with your game when you cant concentrate fire on him
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