This is Fantastic! I'm a little wary of pay as you play though... Maybe allow for the weapon packs to be demo-ed in some way? pictures or descriptions or allowing us the use of them in the firing range.
personally, I think the efficiency mode would've had lives = clips left over, instead of just ticking down every second or two. you can easily pass them by just firing as fast as possible.
A nice TD game. Damn good graphics too. I like that the additions of the second level gives you a shot at quickly building up a defense to take care of those one or two that managed to sneak by.
I'm sick of all these people whining over a game that's actually challenging. The controls work perfectly for the game, and if you don't like them YOU CAN CHANGE THEM. Do people even use option menus anymore?