Icarus: Alien Vanguard 1.0

DOOM is one of the oldest FPSes in existence, and its engine is famously so robust that it can run on pretty much anything and also create pretty much anything.  From FPSes to RPGs to companions to a city living game, it has a ton of different mods and maps that can all do different things. There are even full campaigns created called megawads. One of many is Icarus: Alien Vanguard.

To install Icarus: Alien Vanguard, you need to have ZDoom and move the WAD file into the GZDoom folder, which is pretty par for the course for DOOM maps.

The story of this megaWAD fancies itself a sequel to DOOM 2. Twelve years after that game, Earth's reconstruction began and established a new union to defend itself from hostile aliens. The Icarus, one of the starships of the union, encounters a pocket of hell and gets taken over. You're sent to either reclaim it or destroy it.

It's a more elaborate setup than most megawads. The very premise makes it so there aren't a lot of environments available, but they still manage to put in a variety of different settings. There are ship-based and planet-based levels, as well as virtual simulation levels. There are a bunch of neat mapping tricks used such as simulating forcefields and create depth in space.

Overall, Icarus: Alien Vanguard is one of the more experimental and solid megawads out there. If you want to experience something like that, then you should definitely give this megawad a download.