Not bad
Challenging, in particular in that the use of "tools" was absolutely necessary for winning through, relying on automatic turrets and my own rifle just wasn't enough...
The rifle scope was annoying, though, hiding some of the battlefield with no option to get it down. Animation could also be improved. The "new upgrade available" is a great idea, but maybe should light up something rather than an irritating blink - especially when it's just that I can buy a cheap turret when I already have much better ones...
All in all, enjoyable.