The second expansion pack for Morrowind was developed by Bethesda Softworks and published by their parent company ZeniMax in June of 2003. The first expansion pack was Tribunal.
This, much like the first expansion, is mostly an infusion of new stuff: people, places, and things to bash your enemies' heads in with. The place in question is a new landmass: an island whose name I can't pronounce (but is spelled "Solstheim"), located northwest of the existing landmass. It is pretty sizeable, with an area maybe a sixth that of the big landmass.
The new landmass is mostly covered with snow, which is a very nice change from the main landmass, whose choices of environments are limited to grassland and wasteland. The main denizens of this island are the Nords (think "Nordic"), who have a little village and and little drinking hall. There is also an Imperial fort on the island, which just happens to also be the location of the only dock, with the only fast route of travel to and from the island.
As with the rest of Morrowind and the first expansion, things are very open-ended. There are two "main" quests: you can either help set up a new mine on the island, fighting off werewolves to do so, or you can become a werewolf and fight on the other side. And, of course, there are any number of other quests. The most enjoyable part, however, as it always has been, is to just run around the island and see what there is to see. Find some monsters. Stick them with the pointy end. Explore some caves. Meet interesting people. Kill them. Whatever you want to do, Morrowind is still happy to provide.
This is a very worthwhile expansion. After the endless caves of Tribunal, I admit I was pining for something more open, and Bloodmoon provides enough new open sky to keep me happy for good while longer.