Almost forgot a couple more items: (Beta 21)
Thanks for keeping the golems from growing... it was a nice idea, but more often then not the graphics of the giant golems just got in the way.
The new "Radius" tower is a nice idea. I haven't played with them too much, but the concept of adjusting its range is a great idea.
Some of the older towers, like the Tidal and Quark towers, require too much baby sitting to be used very often. So the radius tower, with its adjustibility and "forget about it" feature is a nice balance of control and effectiviness.