"The Elder Scrolls III: Bloodmoon is the second expansion pack for Bethesda Softworks' The Elder Scrolls III: Morrowind. While it was originally released as an expansion set for Microsoft Windows, Bloodmoon is included within the Morrowind: Game of the Year edition for Microsoft Windows.
Unlike the first expansion Tribunal, which added a city separate from the world map consisting of interior cells, Bloodmoon adds a large new island to the original world map, a cold northern territory named Solstheim. Rather than the Dunmer (dark elves) that are the indigenous race in the nearby Vvardenfell, Solstheim is populated largely by the Nord race. This is largely because the island sits more or less astride the border between Morrowind and the Nord homeland of Skyrim.
This expansion adds new enemies, the East Empire Company as a joinable guild, and the possibility to become a werewolf, akin to the inclusion of vampires seen in Morrowind. Bloodmoon also uses larger and more detailed environments, including snowfall, thus raising the computer hardware requirements, though the ash storms of the original game are much more graphically demanding than the snow of Bloodmoon.
As with Morrowind and Tribunal, Bloodmoon has many side-quests to finish and many caves to explore aside from its main quest. Unlike Tribunal, which is intended to be played after the completion of Morrowind's main-quest, Bloodmoon's main-quest is self-contained within the expansion."
Source: Wikipedia, "The_Elder_Scrolls_III:_Bloodmoon," available under the CC-BY-SA License.