Great little game, but very short, which is the only negative point I have about this game in the series. Alien shooter is an isometric 2D game that floods the screen with often hundreds of aliens to fight at once, requiring you to constantly upgrade your characters stats and kit, kinda like an action RPG. The best thing about the game by far is the array of different weapons, with there always being something else to aim for. You can often make the trade off between very slow but hard hitting weapons (rocket launchers, some of the energy weapons etc) or the opposite scale of extremely fast firing weapons (uzi, machine guns, mini guns, plasma gatlin guns! etc).
Basically, if you get a free evening and all you want to do is mindless violence, this will satisfy your needs nicely!