its awesome even though i don't really understand what's the use of the timer and in the endless mode. when the timer runs out it gets bugged. even the creatures are already dead, the round doesn't end and the enemy mobs still spawns until the flash player crash. hope you fix this. anyway.. it's still a good game.. :D
spoiler tips:
--in mission mode. use 2 fire dragon and 2 entrophy alien, all should be maxed out and you'll finished it with no casualties.
--in endless mode. use 1 entrophy alien, 2 shadow dragon, and 1 spartan, all should be maxed out and using that combo, you'll sure reach round 50+