I like it,but

Way to slow.

and it need to get harder faster.

and that ice tower didnt do shit.

other than that,its a good start.

I gave you a 1

There's plenty of games like this, it's completely unoriginal. There is no sound, and though I don't make flash, I know it's not hard to find sound effects. Also, circles? Couldn't you at least find something other than the most basic shape? It's great for testing but if your going to publish it, make it look better. Also the map layout they travel is rather dull and there is really no set destination for them to go aside from back up, so you don't feel pressured as in "OMG! THERE GONNA GET MY BASE!".

Fun

This makes a refreshing change from shooters. I found myself transfixed at watching the towers shoot the enemies.

All the elements are there to make this a good game. Update the graphics and maybe use tanks instead of circles. Try adding some other graphical effects to make it stand-out. Otherwise I thought this was good.

Unoriginal

Totally stolen idea and not executed the best, the ice tower and poison tower din't really even seem to make an impact which meant the best strategy was to put the first tower at large surface area spots and upgrade to level 2. Also the low amount of spending money and slow movement of the shapes meant that I was waiting for long times as they did a lap back to where the bulk of my guns were.