I have been using the Darkplaces mod, which gives a nice mix of high resolution and graphics support (pretty sure you can turn off excessive filtering if you like the chunky look, wouldn't bother with low-res at this point unless you had an old PC to play it on for the sake of nostalgia, but like many other FPSes high resolution is beneficial) with pretty good compatibility.
Somebody has compiled a list of source ports with compatibility for various mods - it's not as fragmented as the DOOM engines but you also don't get the comprehensive list of flags found in something like zDOOM, either. Not sure how big a problem this is, though - I think Darkplaces runs most everything.
Things to watch out for in mod compatibility are jump height, handling of inertia, and possibly correct treatment of key flags or whatever is used to make progress. I think the only things I've ever noticed are related to jump height.
Mortificator wrote:Speaking of Scourge, this first expansion is a significant improvement to the original game, and probably the Quake-related title I'd most recommend. You wouldn't miss much by skipping straight to it either, I mean, Quake has even less story than Doom.
The second one has a lot of neat stuff going on too.
There are some very memorable levels in the original level set, and if you're dead-set on some old-fashioned FPS fun, I would recommend prioritizing it above a lot of other things. Might as well build up to the climax, huh? Depends on how much time you want to invest in it.
The unofficial / fan-made mod scene is harder to pin down because there's a lot of stuff - some excellent, some terrible. Some of the most visible names:
Abyss of Pandemonium - pretty sure this is decent enough, though not quite on par with the official expansions.
Shrak - not sure I've played it, not a good rep.
Malice - looked cool and has some nice new bullet-points on paper, but not really good to play. Worth a look for the training level perhaps.
Nehahra - this fan-made expansion was machinima'd but I'd play it before wasting time on the video production. Overall, seems pretty decent, though I don't think the mapping was as enjoyable as the official expansions. Story was unnecessary, really.
X-Men - interesting for the weapon transitions and the can't-quite-figure-it-out Nightmare entrance in the hub map, but ugly and bad to play overall.
I have an empty folder for
Quoth but I'm not sure I've messed around with it.
That other retail expansion I can't think of the name of - I've talked about it here - strange and slightly surreal maps with some puzzle elements - was alright to mess around with.
There's many other things besides - probably most of the gems are fan-made modifications made years after people figured out what they were doing.