Well. ESO is going to encompass all of the known area's of the Elder Scrolls universe. So all of the homelands of the Elder Scroll races (so Morrowind, Elswyer, Hammerfell, Skyrim, Cyrodiil, etc) as well as the plains of Oblivion. Technically speaking, the size comparison would probably be similar. But in terms of play area, I think ESO would probably offer more room. The zones are quite vast from what I've experienced