I agree. One thing that I liked with Shadow of Mordor is that it wasn't absurdly dense like some games, but it wasn't barren for long stretches. The map wasn't too big, and if you got bored of running, you could stop off and execute a few enemies, just for the heck of it. To compare, even though I liked Skyrim a lot, you could have long stretches of just running in a straight line through areas too easy for you, and that was tedious.
That is why I hate Fast Travel as well. If your game uses Fast Travel, I see it as acknowledgement that your game's world is full of redundant filler or patches of emptiness. I should want to run around and do stuff, Sunset Overdrive is another where the open world was worth just messing around in. Dying Light was like this, though not in an amazing sense. Watch Dogs had it, but got a bit redundant and boring near the end of the game. The Borderlands games struggled on this, I think. You had to have too many back-and-forth treks through low-level enemies (think the first game's opening area, Fyrestone), and it was sparsely populated.
I both agree and disagree.
With Skyrim, on the one hand, you're creating a world that
needs to feel organic and believable as a true, fantasy realm. Massive forests, multiple settlements, open plains. To really immerse the player that needs to be fleshed out in more ways then simply making the map "look" large with impassable cliffs or unfordable rivers.
One of the biggest complaints leveled against Oblivion, and many MMOs with smaller maps, is the
"theme park" feeling, where everything feels artificial and placed and perfect intervals, like attractions in a theme park, to make sure the player never has to feel like they're not being engaged at all times. While that has its place, the strength of The Elder Scrolls games has always been exploration and atmospheric immersion, and big open worlds are an integral part of that.
On the other hand, I agree with you about fast travel. I've always hated it, and kind of "house rule" out of my games (yes, I know there are mods to completely remove it). I always thought the best solution was the "wagon rides" outside of settlements; reach some kind of town, find the wagon, and pay the requisite fee to get to wherever you're going. In the vanilla game, it's only available outside the major holds, but I downloaded a nice little mod that puts a wagon in or near most settlements. To me, I feel that's the best, most satisfying compromise between fast travelling everywhere, and having to slog across the map for some trinket.