In 2002's Elder Scrolls III, players journeyed to the home location of the Dark Elves, Vvardenfell. In Elder Scrolls Online, players will be in Vvardenfell again or, more accurately (and technically), for the first time. The events of ESO take place 700 years prior to the events of Elder Scrolls III so the landscape is going to be both familiar and different at the same time.
Most notably, cities and villages may or may not be present. For instance, Vivec City is not yet complete, though it will be present and recognizable. But other, smaller, more remote locations may not yet be present in the MMO version of Vvardenfell.
Politics will also play a major role in Morrowind with two houses vying for dominance: Redoran and Telvanni. Hlaalu is not yet a factor in the landscape.
When you enter Vvardenfell in ESO: Morrowind, House Redoran and House Hlaalu administer the south and western regions of the island, and both are members of the Ebonheart Pact. The east of Vvardenfell, however, is firmly under the control of House Telvanni. It's worth noting that because they are not members of the Pact, the Telvanni still practice slavery (primarily of the Argonians and Khajiit), exacerbating tensions between Morrowind and the rest of the Pact.
You can read more about the changes between the two games by visiting the Elder Scrolls Online site.
