Valve are planning to release a Linux version of the online Steam service allowing users of the many disparate Linux distributions to play the many games available on the Steam service. Older games such as Doom are available for Linux, but the actual IWADs that allow you to play the original Doom, Ultimate Doom and Doom2 games are still proprietary property of ID Software and having these available in Steam makes it very easy for a gamer to install and run Doom. This website: http://www.steamgamesonlinux.com/ is a blog that hosts reviews of various games and their playability on Linux. Some games require Wine to run, this sometimes works just fine, and is better than nothing. Obviously, Linux binaries are preferred, but not always available. Unreal Tournament 2004 has Linux binaries, the original Unreal Tournament also has Linux binaries available, but they do not seem to work on a modern x86_64 system. That game is playable with Wine though, at least that is functional. Steam are using Ubuntu 12.04 as a base and they have ported Left For Dead 2 and it is running natively on Linux as outlined on the Steam Linux blog: http://blogs.valvesoftware.com/linux/.
The ID Software game Doom3 is one game that has native Linux binaries allowing easy setup and play on a Personal Computer running Linux. Quake3 is another ID Software game that has Linux binaries available. The ioQuake3 binaries are a better alternative to avoid problems when running on a modern distribution. Enemy Territory Quake Wars is included in the list of native Linux games. I installed the 2.27 patch for the original Unreal single-player game and it included Linux binaries, but they will not run. Unreal Tournament 1 has Linux binaries available here but they will not run on a modern Linux distribution as the libgtk-1.2 libraries are not available since the move to GTK 3.0. That is why Wine is useful for running old games on a modern computer. Doom is one game that has an extensive community that is still creating levels and source ports for it that allow a whole new generation of gamers to enjoy the game that revolutionised PC gaming forever. Sure, Wolfenstein 3D was a first-person shooter, but it was nothing like Doom, that game seemed so realistic in 1994.
This Ubuntu web page: https://help.ubuntu.com/community/Games/NativeNonFreeCommercial has a nice listing of games that will run on Linux, but it is a bit dated. But with the efforts of Valve Software to port games to Linux and the positive comments here: http://blogs.valvesoftware.com/linux/steamd-penguins/#comments the future of gaming is looking very rosy indeed. You will not need virus and malware prone Windows operating systems to run your PC games in the future. The Darkplaces source port for Linux and Windows allows Linux gamers to run Quake on Linux with the ability to use high-resolution textures and high-resolution models, making the game look a million times better. Windows and Linux binaries are supplied together in the package as well as the source code for the Nexuiz and Darkplaces binaries. If you are pedantic enough to want to build a game from source to ensure the binaries are perfectly optimised for your CPU. Get it here: http://icculus.org/twilight/darkplaces/.
This source port is quite demanding when you run it with Real-Time lighting, but the eye candy is worth it. A far cry from playing Quake 1 on a Pentium 1 computer all that time ago.