Awesome
I've played this about 10 times already and I plan on playing more later.
The only problem I have with this game is that the vulcan is useless (you can't shoot if for long enough and it takes too long to get in and out of) and the auto turret is pretty useless as well. The only way I've been able to get a decent score has been using the rifle and grenades alone. After about level 22 or so, it gets ridiculously impossible and there's no possible way to have enough energy to upgrade your core 2 items before you die. Please either make the turret's prices lower or increase their effectiveness.
All in all though, this game is excellent and I like how challenging it is. The different items show a real potential for strategy and different play styles but there is a clear 'best way' to play the game so that part suffers.
The Enemy health scales up really well but by the time the rifle costs 8000 to upgrade, it becomes impossible to survive long enough to upgrade so please decrease this upgrade cost or increase the damage of the previous teirs