Immortal Defense now 'pay what you want'

[youtube=http://www.youtube.com/watch?v=cUC6W9r-Bj8&hl=en_US&fs=1] When it comes to Tower Defense, there are three games in my mind: Defense Grid, Comet Crash, and Immortal Defense. The former is the best by the numbers approach to the genre. Comet Crash makes a lot of interesting