The other day, Kromzul of Burning Blade posted a thread in the official Wrath of the Lich King forum about dungeon design. He asks if instances will be deeper than those in the Burning Crusade, and I agree with most of what he says. Essentially, the epic, sprawling dungeon crawls of old have gone extinct with BC.
Bornakk chimes in to say that The Burning Crusade dungeon design was heavily influenced by player feedback, wishing for more Scarlet Monastery-esque dungeons. I can see that, and to an extent, I agree with that, too. Scarlet Monastery, while shorter and more linear, was also pretty cool.
Personally, I don't think that it really comes down to one or the other. Take Dire Maul, for instance. Each wing could be tackled in a straightforward, linear fashion. However, each of them also had alternative routes, and some of them even had alternative ways of defeating them. For example, Tribute Runs in Dire Maul: North. Plus, they were even connected via the library. If you really want to, you could go from one wing to the other without any loading screen.