desktop tower defense mad

I've finished the game at hard difficulty; for me, it's about getting both waves of enemies to go in the same direction and then trying to get them trapped as long as possible. As the enemies and the creeps get stronger, it's about building up the strong units and the freeze cannons for me, to get them slowed down and continuing to go through my "maze". It can be pretty difficult, but it can be done... I'm still working on the "100" challenge, though. I can get it upto like, level 71 but not much further. It's a crazy one, but I'm getting better. When I first started playing I could only get to the 50th level or so. Good luck to you!