The same could be asked for Quake 1 & 2 :)
The same could be asked for Quake 1 & 2 :)
If you insist on using your CD rather than using a GOG or Steam copy, you'll want to be able to get at a "doom.wad" file. Depending on the CD you have, it'll either be available as a regular file, or compressed as an LHA archive. In the latter case, you'll find either one file such as "RESOURCE.1" which you can extract directly with lhasa, or several files like "DOOM_SE.1", "DOOM_SE.2", etc, in which you'll want to cat them all together into a new "DOOM_SE.lha" file and then extract that.
A list of all active multiplayer servers can be found at http://q2servers.com/. You can usually find people playing action, ctf, deathmatch, and jump mods.
(Source: I still actively play Q2)
ZDoom is one of the most popular source ports capable of running all WADs and it's still being maintained. GZDoom is the OpenGL supported version of ZDoom with new scripting capabilities and GL lights.
For Quake 1 there's the DarkPlaces source port, and for Quake 2 there's Yamagi or Q2PRO.
and then there's Zandronum, which is built on GZDoom and adds modern multiplayer features (servers, in-game joining, etc).
It even had an option to replace the sprites with 3D models, but I found I much preferred the sprites.
It has a few odd non-retro options enabled by default (screen shake on impact and translucent firey projectiles being the main ones that annoyed me, but they're easy enough to disable) but other than this is probably the closest to a "pure" DOOM experience I've had on a modern OS - not counting DOSBOX of course.
It's also Open Source: https://github.com/bradharding/doomretro
Also you might want to check out http://celephais.net/board/news.php which has a ton of very high quality user content for additional chapters, like mini expansion packs. Some really great level designers and artist who are making still making stuff for this game.
I'd say Crispy Doom (or Doomretro on Windows) are good balances.
As for Quake 2, Yamagi Quake II is the best (yamagi.org/quake2)
For Quake 1, tyrquake. I can't remember what I have for Q2.