First Person Shooters have gone through some major changes in the last decade. It is a genre that was once branded as "brain dead, shoot 'em ups". That is certainly not the case anymore. FPS games have spawned million dollar tournaments, user edits, and fantastic plots. Here is a quick rundown of two major players in FPS development.
Bungie: USA. 1991. Founded by two undergrad students from the University of Chicago, this company prides itself on its irreverent attitude towards formal business practices. Their ultimate goal is to nurse and embrace creativity. Their biggest hit, Halo, successfully brought amazing storylines back to traditional first person shooters. When the developing company was acquisitioned by Microsoft, they turned the first installment of the Halo series into a launch title for the original Xbox. It went on to become one of the most successful launch titles ever. Common traits to look for in Bungie games are definitely first person shooters. They are typically based in exotic locations with elaborate story-telling.
Valve: USA. 2003. Valve is a developer that has created several major hits in a very small amount of time. Their biggest hits include the series Counter Strike, Half-Life, and Left for Dead. The company is best known for using the Source engine. While many games rely on backwards compatibility, the Source engine evolves in small increments. So when the developer or actual players create mods, they can carry over to sequels. Common trademarks of Valve games include classic first person shooters. They encourage modifications and frequently develop games that include multiplayer components. Even with all this, they still try to create interactive environments for a great, visceral gaming experience.
Purchasing a game from either company would be an epic win. They are super fun alone or in a group. If you are looking for legendary story, Bungie games are for you. If you want a variety of massive multiplayers, check out the latest Valve game. Better yet, do yourself a major solid and purchase games from both.