This is a truthfully addictive game. ;) Nice concept - very original as plot. The upgrade system is fairly balanced and it requires that good skill-to-luck ratio thanks to the introduction of the enemy soldiers.
However, and this might be just me, I don't quite get the mission objectives. Some are easy, too easy, like the grenade one, which stacks the kills, While for others, like kill X amount of soldier type Y, are a waiting game and keeping your fingers crossed and soldier Y will spawn.
Overall a good solid 5/5 :)