The only quests in the Underworld I've done since the SA expansion went live is Tobin the Tinker's quest for floor traps and Jaacar's quest. I did the quests offered by Gretchen, Neville, Dugan, Flint, and Vernix during the beta and not since then. I haven't done either of the Xenrr or Barreraak quests.
My feedback on the quests:
Garamon quest to enter the Abyss via the Underworld: I like this quest; however, I was very disappointed with how long it took the devs to fix the problems caused by so many people trying to complete the quest in the first few weeks.
Egwexem/Naxatilor quest to enter the Abyss via the Tomb of Kings: Another good quest. However, I'm amazed that over six months after it was introduced, no one has turned on the spawn in the Holy City on the non-Japanese shards!
Percolem the Hunter quests: Love 'em and still working on them. Since I'm such a cheapskate and only recently started working on fishing, these quests and the Axem quests are my sole source of white pearls.
Axem the Curator quests: Another good set of quests. Just wish the pottery fragments were shaped differently or something. Sort of a nuisance to toggle them as quest items when you have a cluttered backpack like I always do.
The Artificer quests: Have only done the lower two quests. Relic fragments....ummmm....haven't owned a one since beta or on Test. Haha. Someday........
Aliabeth: I really wish you took the Valentine's Day white chocolates, dear! Good motivation to keep working on cooking and to visit Ilshenar and collect cooking ingredients from paragons and/or grow cocoa trees for cocoa pulp. Sliem: Keeps me mining and I love those black boxes! Ansikart - Didn't even know he had another quest. Gotta try it out, I guess.
Thepem/Zosilem - For some reason, the ingot conversion stuff just does nothing for me plus I don't think it stacks. Have gotten a few tasty treats but always forget I have them. One of these days I'll remember to take some along on a long hunting expedition.
The quests in the Underworld: Time to actually go do these, I guess. I wish the floor traps had turned out to be more useful because it was kind of exciting to think someone actually came up with a quest for people who worked up the Remove Trap skill. Flint's brew perhaps has potential. Gretchen's probably still the snot she was in beta and I don't know if anyone's figured out how to use her reward yet. Have no use for costumes but maybe the fish would be nice to have if they can be mounted (?). Haven't tried Navrey since she was beefed up on Origin because the loot just wasn't worth it and my luck for getting artifacts seems to be nonexistent so joining the campers is a waste of time. I'd rather go make gold elsewhere and train up pets or skills in the process and buy the artifacts from someone else some day rather than beat my head against the wall while cursing the RNG gods.
Agralem the Bladeweaver: May do it just to get the cyclone and see if it's any good for the gargoyle bladeweaver I'll never make.
Farmer Nash: Maybe fun for killing some time with a low-skilled character....?
Laifem the Weaver: Unless something's changed with what you can safely place on top of the custom carpet, can't see myself completing this quest to buy custom carpeting.
Sutek: Because the mechanical pets don't bond, I haven't been inclined to want to do this quest. It sounded like a fun and challenging quest during the beta, though.
Ortlem: The Crystal Ball of Knowledge is a great item to have and this quest is super-easy. This one's a winner.