Top-Notch
Nice game. Very stylish and smooth. Here's a few suggestions to make a great game better:
1. Include info about guns for example DPS, damage range eg so you can exactly see and compare whether the upgrades are worth morde than building new turrets.
2. Visually alter the turrets based on the amount of upgrades they have recieved. cooler turrets give more incentive to upgrade
3. Can feel a bit slow at times in my opinion, especially between waves. maybe introduce a way to speed up time + earn more bonus points for doing so?
4. Moar weapons. maybe some become unlocked as you proceed through the levels. Assault rifles etc.
Just my two cents, don't get me wrong I think its an amazing game. Just Constructive Praise ^^