I actually like running quake at the lowest resolution that still fits 16:9 screen. Having everything be really blocky kind of adds to the tension because you can't really make things out at a distance so you feel more nervous at points. I also think low resolution helps games with repeating texture walls help make them look more varied visually, because the pixels don't display perfectly, it looks more like a believable surface in that. Getting the music working in the steam version is very important because that soundtrack is so oppressive and great.
I usually play it on normal and I've beaten it on hard before but I think I actually really like the changes to monster spawns on Easy. The game feels more horror focused because there's less ogres and shamblers and more fiends, which are fun to fight and force you to dodge more, rather than hiding from lightning/grenades during every fight.
It makes the game feel more varied because the enemy types get spread out more as a result of using a fiend or zombies in place of the bigger enemies in parts of the levels. You still have to be on your toes, but it feels like you're bobbing and weaving more with the low to mid-tier enemies than the higher tier ones. I kind of wish the spaceport enemies showed up in the hell areas sometimes just so they could mix in with the other types, but maybe that wouldn't have worked out well?
I feel like Vores and Shamblers are the cyber demon/spider mastermind of this game, and could have been "bosses" for early eps that show up later, and I feel they got overused in the normal difficulty. Ogres kind of get placed around pretty leisurely too. I like them being used more sparringly so the lower tier guys get used more. (They're sort of like the hell knights/barons of hell of this game) In some ways you can feel the frustration of the team when they were making quake. You could probably reshuffle things about the campaign to get a more interesting singleplayer experience, though it'd probably be a lovecraft variant of doom's plot anyways if you redesigned the enemy encounters and stages per episode.
Speaking of bosses, Chthon is interesting on easy because they modify his fight so you only do the lightning trick 1 time. Because it's a gimmick fight the 3 time loop never felt that great. Only doing it once feels appropriate to what that "fight" is. I think he should have been the boss of the third realm, and let shambler be the first realm boss, with vore as the second realm boss (With shamblers showing up more commonly in realms 2 and up, and vores in 3 and up). I loved doom 1's (and the end of doom 2) emphasis on having a boss get a real boss stage before they became normal dudes. Big moments like that were cool.
I don't like Doom or Doom 2 on easy but Quake's layouts and horror themes actually kind of work. (Plus with less ogres you have less rockets/grenade ammo drops) It's kind of cool and something I never played before and I bet most players never touched it.