Latest Games
Spider web
Time traveler
Bloxorz - move the block
Stop the Cat - block his run
Ice Slide - make the seal slide
Free the Smilies
Ant Attack - kill the ants 
Shoplifter - steal the goods
Hit the red ball,
Kill the bugs - very good!
Driller - dig your way to victory
Help the Black Knight
Kill The Zombies!
Kill The Zombies #2!
Great little mini golf game
Bow fighter - defend your castle
Small man tries to catch your cursor
BlockBuster a great game
Curveball Game - Pong with style
Bash the penguin
Kitten cannon
The idea here is to place your guns (towers) in such a way to kill all the bugs that come through. Like Lemmings in reverse
I tend to use the Squirt towers and upgrade them making a killing zone around the middle of the board. The Frost towers are good to slow the bugs down, so are good placed near the entrances. But they don't stop the hard big bugs
Fewer towers and more upgrades also seems a good rule of thumb. I notice that you can direct the bugs around so channel them into killing zones.