Many quarters of the internet have just gotten excited by this trailer for Grand Theft Space (read: the trailer came out a few weeks ago, but it's just hit the top of r/games on Reddit so now all us special interest sites have seen it too), and that's because it looks amazing.
Grand Theft Space is still in progress, with no concrete date for release yet, but it has aliens, high tech guns, space vistas, giant planets, moon buggies, and so on. The developers of the mod are currently working on bug fixes and other additions, but it sounds like there will be quests, and at least one alien city to explore.
You can see some gameplay, where a player flies to the moon, and trundles around exploring Mars, in the video below, and some more screens here. Get hype if you like GTAV mods, or space, or both.