#8 Diablo 3
When Diablo III was first announced, there was some worry that the game wouldn't be as vast as Diablo II, which was set in multiple environments across the world of Sanctuary. Thankfully, the third entry in the Diablo franchise managed to surpass expectations with its relatively seamless world that's very neatly divided by the game's four acts.
With no loading screens apart from the one you see when you first start the game, Diablo III not only feels huge—it IS huge. And best of all, it doesn't feel empty.
A lot of action RPGs try to make up with size for what they lack in content, but every part of the Diablo III world feels "lived in". Even the dungeons are explained through journals for why they exist.