This is a short game, but a damn hard one. The shooting lags, so you must know in advance where the enemy will spawn. Had to use the shortest routes, so not to waste energy and ammo. There are only three levels. In the first two levels you need to get a specific weapon from the van (flamethrower for level 1 and grenade launcher for level 2), so you can advance further. The energy resupplies in level 3, and it's ironically the easiest level.