Henry
Autoexreginated
I didn't really start getting into D&D until the end of 4e's life cycle so I am not intimately familiar with the Nentir Vale setting but it has always been the setting that I found interesting, and I love the pantheon so much that I adopted it for my own game. One of the things that I did like about it is that the deities feel more like characters than abstract forces. They play active roles in their mythology and they behave in ways that show their flaws. So from that perspective, humanizing them further by giving them mortal origins somewhat makes sense.
I think the deities included were part of what turned me off, because it reminded me of my early campaigns where I would grab this god from this setting, that god from that setting, make up a few new ones in between because my setting was so unique and original, and call it my own. This "homebrew" feel to it is perhaps where I got the "unoriginal and uninspiring" vibe that the setting gave me at the time. That, plus the total cosmic restructuring that stuck demons in the same places as the elementals and little things like introducing Dragonborn and Tieflings as core races and making them prime movers in the setting, and conflating erinyes and succubi, were all things that went contrary to all that had come before it that annoyed me at the time.
Truth be told, looking back on it now and separating it mentally from all the edition warring that was going on back at the time, it's not a bad setting, and could stand to be fleshed out a bit more. I think its intentional lack of detail has worked against it for my liking, whereas compared to a Krynn, Eberron, Faerun, Oerth, Athas, Golarion, Taldor'ei, etc. their distinctness comes in their features and lore. Athas is another example of a world focused on only one small area in a world of near-oblivion, but the flavor in that small area is extremely detailed and uniform; if Nentir Vale had that level of distinctness for what cultures and events go on in its borders, I think it would have piqued my interest more back when it was released.