I think most people use Diablo because they know 98% of the gaming population will know the reference.
Totally, you hit the point A fast reference that don't need argue to be understood.
I agree, IWD was in between Diablo and BG. And there were fine stories behind some places like the Severed hand. What i disliked was the never ending whole game dungeon. No variety at all. And when the game is just about killing so many monsters and about loot, i use to make this easy comparison with Diablo because everyone undestand why. (The first Diablo was awesome though). I really prefer more varied games like Planescape, Fallout 1&2, Arcanum, BGate,... The 15 lvl dungeon may be great, i'm just afraid that it could be an excuse to push the player to a boring, never ending and non sense monster bashing.
Monster bashing + loot is not "adventures" for me. Just monster bashing + loot. That's why i made the comparison with Diablo and why i made my first post here. No offense.
If the dungeon is intriguing, with cool story, and as varied as the Durlag Tower Stun spoke about, i actually may enjoy it. But probably less than the core game. Just my own way to have fun.
Although I can see where you're coming from, having Od Nua as a "monster bashing + loot" marathon would be fun for a lot of us, especially people like me who played Diablo and Diablo 2 more than then IE games
Variety is the spice of life! Although purposeful adventuring is great, too.