Between searingly-hot laser fire, a myriad of otherworldly aliens baying for blood (or joining up to fight some mysterious force) and getting your own spaceship to bomb around the galaxy in - sci-fi might just be the greatest genre on Earth. In video game form it's journeyed everywhere from the 2D planes of Metroid through the gore-drenched Gears of War series and even across galaxies as we joined Commander Shepard and co. to tackle Mass Effect's Reaper invasion. In short, right next to more atypical fantasy - like the Skyrim/The Witcher-style goblins n' blades variety, it's the only other cross-medium genre that people get well and truly enamoured with. Unlike franchises like Star Trek or Star Wars on the silver screen, there aren't too many landmark series' in gaming with so much weight and purpose. Sure you can point to Bioware's phenomenal Mass Effect trilogy or Valve's Half-Life titles, but when it comes to the tropes of the genre; laser-blasters, crazily-coloured planets and the denizens within - everybody's having a go. Some readers' earliest memories will be the likes of Asteroids or Space Invaders, and alongside 1982's Tron being one of the first major motion pictures to feature gaming at its core, sci-fi is essentially the lifeblood of the medium. So, when you think of the greatest sci-fi games you got totally lost in, were they always the ones that make the top 10 lists of their respective years? Check out our candidates for the best of the rest, and leave your own in the comments below.