I liked it. For all those who can't beat it, here's my strategy:
For the first few days only buy Machine guns(Never buy #1, was a waste of money.) When you can, buy new elevators and fill with as many machine guns as possible. Eventually around like level 5 or something you should be able to buy Rocket Launchers without saving up. Sell one Machine gun or if you have an empty spot in it put it in there. Eventually you'll be able to get Laser cannons. Put them in there so you have 1 Machine Gun, 1 Rocket, and 1 Lase. Fill all elevators like that. Eventually you can start upgrading. It's easy then. Don't upgrade at the very beginning though. =/