IMO you have quite a few balance issues in the weapons. Lightning should be the ulti weapon, not death duck. Rail Gun should have more ammo/more damage, big laser needs to have slightly more ammo, tornado and slow time should probably have slower cooldown times. p.s. you should totally have a health bar that you can see on all time in the UI. You should also be able to upgrade health, for, say, 100.000.
It is too easy. I'll sum up the reasons why quickly, as last time I tried I exceeded the maximum character limit.
You need AA enemy helicopters (to balance things out), you need a slow-moving enemy plane that paradrops infantry unto you, they could also drop AA vehicles. You need the enemy's infantry to look different, and I would suggest changing the apache's missile sound to something lower, less high-pitched. And the AA missile is pointless as of yet, to balance things out you should replace it with something like a cluster air missile (or three missiles at once).
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