I know the game is a bit older but... wow is it PLAGUED with problems.
Now before I start, I have a Geforce GTX 680 Lightning and man does this game lag even on low settings. I'm not sure if it's just because of how Flash had been updating as of late, but I don't think the military has to worry about killing me at all: the lag will do it for them. 70% of all deaths is PURELY from lag in later areas. On Low Settings. On a overclocked graphics card.
So why keep playing? Well I didn't say the game sucked; in fact it's impressive! It has that 'one more go' feel and that is what has kept me playing despite the lag. Even mapped it to a wheel controller for the lulz.
The cons? Well, the helicopters can go the hell for all I care. I get they are a mechanic in the game, but the issue with them is that their hitbox is atrocious. The remaining 30% of deaths is PURELY because the game doesn't feel like giving me any hits when I clearly had them. This is the biggest con of them all. Carpet bombs? Even without the HUD thing, they're a nice twitch mechanic. Soldiers? It keeps things in check and works fine. Mutated Zombies? Annoying but acceptable. Just the Helicopters. They're broken.
Overall, it's a great game. The upgrades could have been more broken apart (instead of 3 tiers, have 5 but keep current maxes), but that is just a matter of opinion. Everything is great.
Except the Helicopters.