New screenshot:

I have created two new tower types

Poison towers: the green ones, poison enemies which drains their life for some period of time
Stun towers: Brownish-red ones, damage enemies and have a chance to cause them to not move for some time

in addition to the old ones:

Der Basic towers: white ones, can be upgraded to become obliterators (more on this in future posts)
Ground Pounder towers: Orange ones, powerful towers that upgrade to fire rapidly

The blue and red rectangles are the enemies.