Zombie Shooter is...not bad.

I've played several of their games. They aren't bad, but play one and ignore the rest, as the only differences seem to be the title and enemy graphics.

I remember playing the demo to Alien Shooter so many times. I recall Zombie Shooter being basically that but zombies.

Still, they're all fun games.

The shooter series games are quite good, especially near the end game when you're fighting thousands of aliens/zombies at once. Survival mode is quite fun too, even though I usually don't like arena based games.

its decent but it gets repetitive after a while well at least alien shooter music fits the game better

I finished Alien Shooter. It's ok.
My main complaint, once you get to the second-to-last level, the final gun is required. You can run through your entire inventory of ammo for all other guns put together and it won't clear the first room. The final gun mows down everything in the level with ease.

The original Alien Shooter became a slog real quickly due to the endless acid spitters constantly spawning. Fuck that waste of gameplay. The update was much better so long as you are cheap on the upgrades and save for the best gun, before you play the stage with several teleporters endlessly spawning waves of monsters. If you don't rage in disgust, the last stage is rather brilliant if pasted many times.

AS2 is just plain great for both versions, though Reloaded has a few extra stages to help get you a few more levels to better balance the next stages. You control gatling guns, nuclear powered tank, and get drones.
I must play Conscription at some point.

ZS1 is short and still good. Dual pistols with full upgrades are like machine guns. Music is weird and works well.
ZS2 is incomplete garbage and places that look like secrets are holes in the map.