I find it so interesting that people hate The Nin-in-Eilph so much. I've always thought it was one of the better quests.
I'm not surprised at all. It's got quest stages that wipe your progress every couple rounds. That's a recipe for hatred, with Nalir as the cherry on top.
I think quests that focus only on the elements, like Nin-in-Eilph or the Old Forest, will score pretty low. If there's only 5 Enemies in a 40-card encounter deck, people are only going to get bored or location-locked. Those quests, while thematic, aren't a good experience.
I think they are fun. Mindlessly slaying orcs is fun on occasion, but that also gets boring and is usually pretty easy to deal with. There are only so many location quests which are a nice change of pace. The real reason I like The Nin-in-Eilph is because of the quest stage variability, though. Making a deck that is consistently good against it when you don't know what the first quest stage will be is a different kind of challenge, especially since 2/3 of the stage 2s are particularly punishing.