In general I agree with this as dungeons should be different size and as much as you do need small quick in and out caves etc. I look forward to completing an epic dungeon.
I have a slight concern though that some of you may be able to clear up as I can’t remember how it worked in Oblivion as I haven’t played that in years, but I am currently playing Morrowind and I don’t think huge 2 hour+ dungeons would work in that game.
In Morrowind; if you go into a dungeon, kill everything and then leave; only to return again; the dungeon is filled with creatures again. This sort of means that you want to finish the whole dungeon in one go. The problem with this is that if a dungeon will take 2 hours+ to finish; I would expect lots of items and people to kill which may all be carrying weapons and armour etc.
I seem to remember in Oblivion while doing dungeons; if my carry capacity was full, I could just run home to drop everything off and then return to the dungeon to finish it.
If creatures will re-appear after leaving then you would have to empty the dungeon and then pick a selection of the loot to keep as the rest would disappear. I hope it’s like I mentioned with Oblivion how you can leave without more creatures appearing.
On a slightly different note; I think it may be fun to find a huge dungeon someone that you have emptied and then claim it for your home; I’m sure there would be plenty of chests etc. to store stuff as long as the entrance is somewhere not to far away to travel to.