Shivering Isles is just what a hardcore Elder Scrolls fan wants with an expansion pack.
Although the gameplay hasn't changed, the artistical area of the game truly have. Shivering Isles is both a colorful and dark realm, and should remind many of Morrowind, which had strange and unique landscapes to itself. The engine has not been improved, but that doesn't matter much, as the expansion is truly different with strange new enemies. The reason this score is an 8 is because I have experienced quite a few moments with a choppier framerate than Oblivion normally has, which should not be happening, although you will forgive it anyway.
The sound in the Isles is again, basically the same as before. It is too bad they did not add some new music, and the old kind does really not seem to fit the mad theme of the Isles. That is just minor nitpicking however.
The value is great for an expansion pack. Shivering Isles will draw you right back into Oblivion for even more gameplay hours, which I didn't think was possible after playing 200 hours of Oblivion beforehand. It is well worth it because of the quest content, new NPC's, dungeons, and items that will in all make this larger then a normal full-priced game. Shivering Isles is worth the trip back into Oblivion, if you were aching to see something new and different besides Cyrodiil's forests and castles, the Shivering Isles is the place to go.