Greetings,
This thread is not about homebrewing from whole cloth. It is about folks that take known settings such as the numerous ones from D&D, and IPs such as Starwars, Marvel/DC, Alien, Game of Thrones, etc.. and make their own content. For folks who do this, do you cleave as close to lore as possible? Or do you take the foundation and run with it? Universal generic system or custom bespoke? What is your process?
I love to run setting adaptations to RPGs.
I prefer to use official systems, if only for the reduction of arguments in, "But it doesn't work that way!!!" angry arguments. And have found that ports to existing systems usually suck more than a NASA Vacuum pump.
Star Wars: I never tried to run SW using anything but official systems. Loved WEG, but now only like it, and preference is for 2.0, NOT 2 RE. WEG d6 Space was essentially 3.0; the 2.x templates work just fine with it. Prefer FFG. Hated d20, and only later on looked at Saga Edition; hate most of the conceptual choices
for Star Wars, tho not of need bad. And what I've heard from friends running SWSE really reinforces that. They liked it, what they were doing felt totally unlike anything star wars to me. I prefer to do Rebel Alliance games, but have run desperate Ne'er-do-wells working for Hutts a few times.
Star Trek: I've run FASA 1E and 2E, LUG TNG+DS9, but never TOS/Voy. Run one one-shot of Decipher Trek, and wasn't thrilled with the clear d20 altered to 2d6 (3rd d6 on nat 12), but it's playable; the setting handling was excellent, tho'. 2d20? I like it better than the others, but LUG with a few changes is equally appealing to me. I don't like the 6 disciplines model; I'd have far preferred a more skill-based approach as was used in Conan, MC3 or Fallout... And I don't much care for the character gen being "all officers Ensign to Captain have the same total competency"...
I've no real issues writing trek adventures, and the Trek Setting is so well known I have little issue with players not knowing some of the basics.
I have tried running Trek with MegaTraveller - the conversion was straightforward, but the system did not help get the feel.
Alternate Trek: The Star Fleet Universe: I love Prime Directive 1e - it's Trek does Seal Team. it's also complex, and char gen a touch mathy... It's just as easy to run as STA or LUG-Trek... but not as easy to get characters generated.
Babylon 5: given that I thought each port sucked... CHameleon Ecclectic's was just too deadly. And had the "all PCs start equal" thing. D20? F that. Traveller? if it hadn't been hamfisted, it might have worked. Adventures? a little bit harder.
Judge Dredd: most of my players for it have barely been familiar with it. I've run the GW and Traveller ports; the d20 port got to char gen and my players said No. The Traveller port? character gen almost killed the one 1-shot... and playing it did. Most of my one-shots of GW use the random block search and hare off into whatever ... so improv on the fly with table support.
ElfQuest: one of the few ports to a universal that was good, IMO. Adventure support, however, was lacking. ElfWar was good... but not enticing to my players.
Marvel... I stick to published adventures, and to two editions: AMSH or MHRP. I found MU mechanics painful, and so it never got past a 1p conceptual test. MM? My players saw the sheet and essentially in unison cried, "Oh, hell, No!!!"
Alien: I've run both the Aliens Adventure Game (PC Light) and the Alien RPG (YZE). The first, which is Phoenix Command Light, was passable as a bug hunt for combat obsessed players, lots of detail... but I've run one minicampaign, once, 30 years ago. And had no desire since to run it. Alien (YZE), I've run 3 campaigns, plus 3 cinematics of the 4, one of them multiple times. It hits the tone right, and enforces some elements of it. Plus, it has just enough random table material to make it fairly easy to run campaigns without needing to be overly creative.
FOr Traveller, I completely ignore everything past TNE's end. I don't much care for the TNE setting destruction, but, aside from damage, I like it. What I've seen of the work coming out of mongoose makes me convinced not buying the rest is a good choice. I had some fun with 1E, but it didn't do the OTU all that well, at least not for me. And when I run Traveller, I prefer to run the OTU - my first experiences were OTU... I've run almost every GDW CT adventure save Alien Realms (as I didn't have it until Marc gave me it in PDF) and Tarsus (as it never appealed, and I didn't have it, either).
T4, I didn't care for the core mechanic, and didn't care for the continued use of FF&S, didn't care for the Year Zero setting... the only part I did like was the Psionics rules.
And, going forward, Alien's displaced Traveller for my Space Shipper needs.
For SG1: I got the D&D 5E derived one from Wyvern. It's sufficiently different from 5E to actually work. I didn't buy the official adventures, and had little issue coming up with adventures. I liked it.
For Tolkien: I have trouble writing suitable adventures...
MERP: The adventure I got was fine, but the system felt wrong for Tolkien. As Rolemaster Lite, however, it works fine.
Decipher LOTR: never got it past char gen. My players said "No."
The One RIng 1E: when I get the urge, it's got a great system and great adventures.
TOR 2E: I hated EVERY mechanical change made. Plus, it put combat into easy mode.... a relatively fresh starting party (no one yet having raised any combat skills nor Valor/Wisdom) took out a full on wraith... and won.
BTVS/Angel: The system's not bad. Adventures aren't hard to write, but doing them well had a greater than 1:1 prep

lay for me... haven't gone back, but ran a fun campaign of it once, got my money's worth.
Army of Darkness: Same system as Buffy/Angel. Haven't convinced anyone to play it.
D&D settings: preferred to homebrew for AD&D, used Mystara but with little reguard for authenticity to lore... Much to Peter's annoyance on several occasions. Love the Gonzo.
Like Dragonlance, my players never seemed to love it.