When comparing X-COM: UFO Defense vs Alien Swarm, the Slant community recommends X-COM: UFO Defense for most people. In the question“What are the best PC games similar to XCOM?” X-COM: UFO Defense is ranked 5th while Alien Swarm is ranked 6th. The most important reason people chose X-COM: UFO Defense is:
Keeping track of more than a dozen soldiers with 10 skills, their inventories (including ammo count and weight), dynamic visibility, line of sight, destructible terrain, consequences of missed shots (like friendly fire or destroyed loot), etc. quickly overwhelms noobies, putting the real strategy masters in the limelight. And this is just a battle out of many, with base building, personell management, logistics, reconnaissance, research and manufacturing between them.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Very deep strategy
Keeping track of more than a dozen soldiers with 10 skills, their inventories (including ammo count and weight), dynamic visibility, line of sight, destructible terrain, consequences of missed shots (like friendly fire or destroyed loot), etc. quickly overwhelms noobies, putting the real strategy masters in the limelight. And this is just a battle out of many, with base building, personell management, logistics, reconnaissance, research and manufacturing between them.
Pro Active open source clone
The openxcom team have re-implemented the entire game and fixed many of the longstanding bugs in the original. It allows you to play on modern machines and in much higher resolution. A copy of the original game is still required for the assets.
Pro Dark humor
Seems to have started the "evil aliens" trend.
Pro Easy to pick up and play, even for beginners
The game consists of tried-and-true top-down shooter mechanics that will be familiar to most players; it is reminiscent of older arcade and console shooters.
Pro Anyone can download and play the game as it is free-to-play and open-source
The game is completely free and has no microtransactions or ads.
The source code is also free and accessible, so the game can be easily modded.
Pro Easily play with up to 4-players in online co-op
Alien Swarm allows for up to 4-player online co-op, which makes for an easy way to play with a small group of friends or strangers.
Pro Convenient offline LAN support
Alien Swarm offers offline LAN (local area network) support, meaning that the game can be easily played locally with each machine connected together in the same place.
Cons
Con Artwork
The artwork is not to everyone's liking.
Con Can get a bit repetitive
The gameplay doesn't change much from mission to mission; you’re generally just shooting aliens over and over again.
Con Gameplay is too short
The main story only takes about three or four hours to complete, which means you could beat the game in one sitting pretty easily.