Great game. Graphics work well, gameplay is fun for a tower defense, good visual clarity.
One suggestion would be to increase the time before the first wave. There's not enough time to set things up and it took me several restarts to get going, especially if one wants to beat the first wave without losing any cores.
Also, not sure if it was just me, but I feel like the v-tower is not worth it because of the 'no other towers' rule. I think stacking the line with lasers is more efficient.