Damn, this is cool looking! A zombie based tower defense game for WP7, where you place survivors to try and attack incoming waves of the undead. With ample Shaun of the Dead references thrown in for good measure. Made by a three man team using XNA, it shows off pretty well what a small crew can make, and the 3D capabilities of WP7.
Plus zombie killing, which is always a good thing.
Day one purchase, or day one purchase?