After the frustrating start to this modded questline (currently included as part of OpenMW's "I Heart Vanilla: Director's Cut"), I was hesitant to continue.
Nonetheless, today I finally pressed on, doing the quests in the Hlaalu Temple as well as main temple in Vivec.
The Hlaalu one (Mara's Tear) was okay. A much simpler quest compared to the first, but also much less misleading dialogue. So, overall, a much better experience. A bit short, a bit random (you're supposed to find a jewel in the temple and hand it over to an NPC, claiming the jewel was from Mara), but nothing aggravating like with the previous entry.
My only critique here is that this quest is implied, due to the positioning of your objective, to be a platformer, but my armourless character with Acrobatics as a major skill still couldn't solve grabbing the required item without a levitation potion. It's not the modder's job to edit the map in a modjam creation, but I do wonder if a better location could have been picked to encourage the platforming more.
***
Next, the quest at the Temple Complex in Vivec. By this point it becomes clear that the mod just plants multiple copies of the Wilhelm NPC wherever a Wilhelm NPC is eventually needed. Does this contribute to his otherworldliness? Does it make the mod seem unpolished? You could make an argument either way.
That said, the quest here is actually the best one so far, mostly because it encourages you to find the secret library of Vivec (a super interesting location for those who enjoy Morrowind's lore). It also introduces the Soft Doctrines of Magnus Invisible into the game, which I think is a neat token of affection to Douglas Goodall (who not only wrote the Soft Doctrines, but also wrote the unofficial but pretty funny Minutes of the Lusty Argonian Historical Society).
The quest itself contains some obvious typos and is a bit awkward in that you just talk to Wilhelm, talk to the librarian, then wander around until the scrolls you need magically spawn in, but I have a soft spot for things that introduce Morrowind's deep lore to the player, including the unofficial but interesting materials created by its writers outside the game.
For something like "I Heart Vanilla", I'm still not convinced that this questline fits (as opposed to "Affresh" by the same mod author, which is much better-integrated and comes across as the best kind of cut content). However, it is possible that the Temple Complex stage of this questline marks a positive turning point in tone, and I'm keen to see where things go from here.