Good for a Beta
Not bad considering its a beta. Some suggestions for future versions 2 "Final" upgrades per turret instead of one, new fields such as a desert field with rocks and stuff to block maybe more then one type of alien per level would be nice like add some air aliens to each wave (not the friggin godzilla sized ones) and let players control the turrets more directly also increase the time limit on each lvl. very fun and can get alot better too.