Vintage FPS games

[Sexbad]

Almost forgot, FreeSpace series. It's not really an FPS, rather a space sim, but it's from the first person and you shoot things. I consider FreeSpace 2 to be the best game of all time, and the source code was released for FreeSpace 2 so a bunch of people got on modding its graphics and making their own campaigns, including ports of the original Descent: FreeSpace and it's expansion pack, Silent Threat.

Technically, you'd only have to get FreeSpace 2 and the source code project in order to play all three games, but I've heard you only have to download the SCP by itself. Either way, http://gog.com/en/gamecard/freespace_2

The feeling of the games is what makes them very unique. You're part of a military organization and it shows. Instead of being sent out alone to do a job you normally have (really smart) AI companions and capitol ships and quite a few times you'll be recalled and replaced by different wings of ships, so that it feels like you're part of the great machine, instead of the amazing video game stylized hero.