When looking at mod-added quests, what are you looking for, and what do you think there should be more of? I considered doing a poll, but there are so many variables here that I thought it best just to hear peoples opinions.

If you're having trouble, here are just a few options to judge your ideal quest by:

Serious or humorous?

Divine or mundane?

Mystery or straightforward?

Combat or no?

Happy endings or sad?

Conclusive or open-ended?

What for subject matter? Politics? Good versus evil? Lore-heavy? Character-focused?

I think there needs to be more larger quest mods in general. Not a simple single quest, but I'm also not asking for massive new lands mods. Just a few quests that tie together and are fun and well made. As for your catagories:

I prefer serious quests. They can have humor in them, and I actually applaud well written humor, but a comedy movie in quest form type thing wouldn't appeal to me.

Quests of all 'scales'. Focus doesn't matter as long as it's well written and interesting in other ways. It can be helping some guy plant crops for all I care, if I have an interest in doing it I'm all for it.

Again, both. Mystery is good, if well written, and straight forward can be just as good if well written. If it's a really dry 'Go here for no reason', 'okay now go here for a single line of dialogue for no reason' then it would svck. But liven things up and keep it interested and straightforward is just fine. However, a mystery quest that's pointlessly confusing and hard to follow can be very bad. you want to gently pull the player along, not speed away down the road without them.

Combat is fine. A quest that's entirely combat would be hard to keep interesting without really good design. Same with a quest that's nothing but dialogue. Again, if well done either is fine, I suggest a variety if you are adding more than a single quest. Change the pace and mix it up.

Happy and sad endings mixed, again. Either is okay as long as it makes sense and feels fulfilling.

I prefer conclusive, unless intentionally left open ended. If it's a cliff hanger and you'll be making an expansion for your mod that picks up where you left off, that can be good. If it just pointlessly trails off into an open ended nothingness and leaves me with an empty unfulfilled feeling though, that's very bad.

For subject matter, get creative. Again as long as the story is interesting and well written, and it's a fulfilling experience it can be about just about anything you can imagine.

Hopefully this helps.

-Mystery quests where it's not obvious at the start who the culprit is.
-Being challenged by riddles. Always a good one.
-I really love 8-10 quests long storylines which surround an entire town (like Morrowind's Raven Rock EEC questline).

Either happy or sad endings - as long as it's well written

Uh, all of the above? Seriously, I was thinking about what kind of quests I would like to see earlier today. I am trying out a character that does not require lots of killing and looting to level up. You know, just some regular Nord guy/gal that's trying to survive in Skyrim. With the help of a mod, he did managed to get close to level 10 on mostly speech but it's getting harder to go much further. I did do stuff like the Book of Love and other fetch and delivery type quests but there are only so many of those before you have to kill somebody.

I was thinking it might be fun to play as a private investigator type of character. You could have an on-going series of cases where you solved murders, find missing persons/items, gather evidence on a cheating spouse, whatever.

I'm in the trenches now creation 16 new quests that center around the mages guild.

I like to write all kinds of quests. I like love story quests that have depth and emotion. While I'm doing a sort of humorous quest, it isn't a silly humor, for skyrim I think it should be fairly serious bizness. For me though, I don't like 20 minute quest mods, unless they are really well done. Very long, in depth, well written, very long quests for me.

and of course I love mystery, so 6 of the quests i'm doing are basically like a pseudo detective story tied into the mages guild. I don't think there is near enough of them in the vanilla beth games. And they have the perfect games for them.

Quests with choices, allowing multiple possible outcomes and/or more ways to achieve the objective (possibly tied to character's skills, abilities - for instance, by using skill checks - and previous choices he made). The choices made in one quest may also have delayed consequences in later quests (e.g. someone coming to your aid in a quest because you helped him in an earlier one).