Everything from Sigma teams is pretty much the same type of game with very little changes between the series.
While that sounds bad they are what they are and if you like this you will like them all. Definitely a sale grab if you can get them all at once for a good price

For a fun 15 minutes of action this game has become my go to. There's not much to it, you run around grabbing different weapons, shoot hordes of easy to kill aliens and survive for as long as you can. I picked it up on sale for £1, and I've been having a great time with it.

Don't go in expecting too much, its your basic shooter from the early 2000s but its a good bit of retro fun :)

Total nostalgic trip !! grew up with this game, and enjoying it once again just as much as I did when I was a kid.