The concept is good; it's a simple little game and it could be very fun, but sadly the dumb AI and absolute atrocious spawn points ruin any shred of immersion. Let me give you some examples. You're in a jungle. Some zombie-like creatures shamble towards you. A big group of them. You unload dozens of bullets from your machine gun. They fall, their blood splattering everywhere. But as they came towards you some of them got "stuck" in the trees. Because of the angle you can't tell they are there. You think you killed everything. So you walk forward and get attacked by the ones that are still alive because they were too dumb to walk around the trees. Their stupidity saved them and hurt you. And it's not just the zombies. Most enemies in this game will stop advancing if they don't see you. So if you go around the corner, they will just stop dead in their tracks until you pop out again. Here's another example: You go down a narrow passage and mow down all enemies. You get to an open area but fast, dangerous enemies come towards you. You open fire on them and retreat down the passage behind you that you JUST CLEARED LITERALLY 5 SECONDS AGO. But you get attacked by enemies that have spawned there. Why? Because **** you that's why! Situations like these are all through the game. Every time you clear an area and move on and encounter new enemies and want to retreat, the area has new enemies that spawn there. It's like the developer has a fear that if there are no new enemies surrounding you every 2 seconds you will get bored. Unfortunately this just makes the game shallower and frustrating. It takes a fun little shooter, sucks out the tactics out of it and turns it into a brainless shooter. Sometimes less is more. If you want a much better game in the same spirit of things, try the old Alien Shooter series. They are cheaper, too!
