I am not a fan of traditional long dungeons. Usually they are not very visually interesting. If fast travel is disabled, then you either have to leave your loot behind or walk back a long ways to sell it.
I mean, you don't have to pick up every single piece of loot that you pass by? Especially if these dungeons happen in Act 2+, we'll already have quite a bit of gold and so carrying out looted armor and weapons from enemies, as well as other low-cost items won't really be worth it. BG3 seems fairly generous with carrying capacity, so I don't really forsee a problem unless you're a hoarder and/or the dungeon is over 30 rooms.
There's no reason why a dungeon can't be visually interesting. That's entirely up to Larian, and they do seem to place a priority on graphics/cinematics. To be clear, by "dungeon" we don't necessarily mean "a system of caves or unadorned stone walls." It could be an ancient temple complex, even a whole buried collapsed city, or some place created by a powerful mage with thematic rooms and outside scenery, etc.
