Agree with shadowbot. No amount of strategy can account for random baddies flying across the screen and losing the game. I've lost the last wave now four times from flying machines. It really adds a level of frustration that dampens an otherwise great game.
dire: There's a yellow arrow on the bottom left hand of the map screen. Click that and it'll bring up a numberical list of the waves. Clicking on a wave number will show you strengths and weaknesses as well as special properties.
 "Parachute Retrospect"){kind=icon}
 "Dungeon Defender"){kind=icon}
 "Generic Defense Game"){kind=icon}
 "The Fancy Pants Adventures"){kind=icon}
 "Momentum Missile Mayhem 2"){kind=icon}
 "Protector"){kind=icon}
 "Fancy Pants Adventure: World 2"){kind=icon}