Perfect!
Everything I could expect from a tower defense game and more.
It had a plot which was fantastic too!
It was difficult, but after a couple hours I've beaten it, with some help from the walkthrough on some levels.
The upgrades were great, and there were a great deal of combinations with the different "towers" available to the player.
Kudos to you sir! A truely magnificent TD game!
Will be hoping for a sequel for me to sink my teeth into, a very tasty game. :)