So far some things that I've noticed (easy mode):
In the very beginning:
- live off your interest and accumulate money
- create many cheap arrow towers
- don't upgrade towers
- try to create a kill zone around the middle path, leave some holes for ice towers
- keep what you've built somewhat balanced, since monsters have resistances to different kinds of towers, so if you build all cannon towers thinking they're stronger, on some levels you'll get creamed -- i start with about 2:1 arrow:cannon ratio or so.
In the middle game:
- I buy ice towers and add them to the kill zone on the middle path
- also build up a kill zone on the first loop up towards the middle and the last loop down towards the middle
- when you start getting enough interest to upgrade the ice towers to level 2 it pays to do that, because you get not only the bonus of more damage from the tower, but it slows them down more and they absorb more damage from everything else.
- i used quite a few magic towers, but didn't upgrade them at all until the very end.
- the initial arrow towers you built should get upgraded to level 3 because they're cheap.
Towards the end:
- I planned out how i put down towers arranging enough room to put ice towers at level 2 all around the circuit to slow monsters down. there shouldn't be anyplace in the circuit where they can accellerate
- I didn't use quake towers, storm towers or water towers at all.
For the last level:
- I had a pile of cash at this point, so I filled up remaining slots with cannon towers and ice towers. the arrow and cannon towers i upgraded to level 3, magic and ice towers i had all upgraded to level 2.
I have no idea how you get a million points in this game like in the network high scores -- i only got a little over 4,000...