The difference is, for me, and most people I've talked to about it, is the feeling of a living breathing world, rather than a world extremely small.
Cyrodill is actually bigger than Vvardenfell, but can you honestly say it feels that way? Nope, because you don't walk anywhere, or travel town to town, you simply warp instantly everywhere, therefore diminishing the feeling of an active, real world.
And Saint_Jiub, I'm sorry but I shouldn't have to "imagine" things like that. It's a gameflaw, and shouldn't be incorporated into the next game without a toggle to turn it on and off.
Ah, I see your point about it feeling more like a "living, breathing world".
I think the major factor is that Cyrodiil sort-of feels smaller because there aren't really any obstacles. You don't have huge mountains jutting out of the ground, or an area you have to move around in the middle. I mean, yeah, fast travel does make the world sort-of feel smaller, but I think there were a few other effects. There was the increased walking speed, the horses, etc. In a sense though, fast-travel can make the world feel much larger. If you only use fast travel to travel between cities you have no idea what's out there in the wilderness, I remember that from my first time playing the game. Destinations felt like they were miles away if you weren't used to walking.
I think that Bethesda's learned from this, but also we'll be playing in a mountainous region full of obstacles (if it's Skyrim
). You've got frozen lakes with vampires lurking under them, the highest peaks of Tamriel, canyons, valleys, etc. I also hope for a method of traveling different than fast-travel, but Cyrodiil was shaped sort-of like a ramp with raised edges. It does actually feel smaller than Morrowind, I agree. When you travel in Morrowind it feels like it takes Ages to reach somewhere on foot, but again, that may be the increased walking speed and the horses. But what I'm trying to say is that Cyrodiil was bound to feel smaller for many reasons, and fast-travel certainly didn't make Fallout 3 feel small. I felt like I'd never reach another city once I set out.
Speaking of which, is the game-world of Fallout 3 larger than Oblivion's? I'm curious.