Great programming, Graphics could be way better...

Great game, very good. My ONE AND ONLY concern about the gameplay is the helecopters... They hover right over the enemy. You need to add code such as
var enemy;
if instance_exists(obj_enemy)
{enemy = instance_nearest(x,y,obj_enemy)
}
if distance_to_point(enemy.x,enemy.y) > 300 //if its too far away
{speed = 5
direction = point_direction(x,y,enemy.x,enemy.y) //really basic movement, id never use it but you get the point
}
else // if theyre too close
{speed = -5
direction = point_direction(x,y,enemy.x,enemy.y) //really basic movement, id never use it but you get the point
}

Or whatever.
GRAPHICS:
why! You used the regestered effects and particles! I know your capable of more than that. Use blend modes etc for explosions (like in fluffum war) and fire. Have seperate randomly placed bushes and shrubs so you dont get stuck with the bad grass. Have bullets fly faster and use advanced collision checking (if you dont know what I mean PM me). Also you could put in lights, etc. The graphics make the game look bad, BUT ITS A REALLY GOOD GAME!!!
so keep working!
SunnyKatt (AKA Zeke games (should be spelled ZekeGames) at TGC forums)
Keep working and fix up those graphics!