According to a posting on the official Elder Scrolls forums, the February issue of PC Gamer features a two-page preview of an unannounced Oblivion expansion called Shivering Isles.
Expansions are always difficult for a developer, as giving the same is boring, and departing from the established too much alienates fans.
In an attempt to avoid this conundrum, the expansion for the popular Elder Scrolls IV will add a unique twist to the established formula - it changes little gameplay wise, but adds a whole lot of totally new and unique content.
Rather than expand into another province of Tamriel, Bethesda dipped into the lore and decided to transport players to the 'Shivering Isles' known also as 'The realm of Madness', the daedric realm ruled by the prince Sheogorath. (Just on a side note, if anyone has the played the Sheogorath Shrine Quests, they should set the tone for the expansion - twisted and at times sadistic humor).
The god Juggalef is preparing his 'once-in-an-eon' Greymarch - a cleansing of the land and everyone within, including, by extension, Sheogorath himself. With this premise you are allowed entry to the shivering isles, a place where everything is a bit off - including the plants, landscapes, creatures and NPCs.
The strangeness of the Shivering isles creates a lot of humor - "Not only are a lot of the NPCs downright hilarious, thanks to the insanity that permeates the land, but the humor also lends something of a clasic LucasArts adventure game bent to the Quests you'll embark upon. You'll laugh more in 10 hours with Shivering isles than you did with 100 hours with the parent game".
One quest has you deciding the fate of a group of adventurers who have strayed into a dungeon in search of great riches. You, along with one of Sheogoraths minions get to decide the fate of said adventurers, as Sheogorath has already decided that they are to die. You can kill them outright, or use traps and illusions within the dungeons to drive them insane (ie the adventurers see a locked cage filled with unimaginable riches - you can opt to electrify the cage, killing anyone who touches it, walk in and kill them yourself, or drop thousands of key in the room, driving them insane as they search for the real one).
You will be able to move between cyrodiil and the Shivering Isles at will, and the expansion will be suitable for all level ranges (I guess this means leveled content), with the entrance to the isles located on an island in Niben bay, near Bravil. Ill close with this quote - "If you're still pursing your lips at the thought of playing Oblivion in a land filled with a pink night sky and trees that look lifted from an acid junkies sketchbook, ask yourself if you really wanted more of the same".