Halo is the on-going series based in SPACE (yeah!) and is styled as a futuristic FPS, covering the war between humans (of course) and aliens (The Covenant).
This is a very famous series, already having 5 titles under it’s belt, and that’s not counting the spin-offs and anniversary games. While I personally haven’t played Halo yet, I’m definitely given it a try because, come on, it’s space (and I need something to distract me from Mass Effect) so I can’t give you my full opinion yet but once I have, I’ll definitely highlight it’s features whether good or bad.
I would detail the plot but there’s too much to cover but I;m guessing you wouldn’t be reading this unless you’ve actually played the game.