Too easy
usually when you can get through a game like this in your first try without a single bit of knowledge of what coming at you it usually means it's too easy.
Very good game but...
You might wanna change a few things, like what the nuke good for? seriously i used ti once just because it was a nuke and i thought it was pretty weak....I mean i can do the same job with my basic pistol. Shotgun was also pretty useless unless you had a huge bunch of light infantry coming at you and still...a few headshots with your pistol and you had the same result as with a bigger gun. Rockets and rifle we're ok, they we're usefull.
If you intend to make a sequel or just another completly different defense game just try balancing it more and you'll have a great game.
Anyway good job!