Yes. Welcome the return of the horribly designed creature and loot scaling. This topic has beaten to death far too much, so I won't get too much into it. Basically, the terrible scaling system encourages "backwards" character design, suppression of level gaining, and can result in some annoying immersion breakers. For some reason, though, the scaling seems to be somewhat less annoying in the Shivering Isles, with the addition of quite a few unique items and less obvious NPC scaling issues (no armies of glass armor wearing bandits to stick out).
The rest of the gameplay is exactly the same as Oblivion, for better or worse. I won't rehash any of this, since it has already been covered extensively in Oblivion reviews.
Let us get one thing straight right off the mark: this is not Oblivion in slightly different terrain. The missions and quests in Shivering Isles are not a rehash of adventures that will feel all too familiar; instead, Bethesda have created all-new missions and dungeons that have features unseen in Oblivion and that are much more story-oriented. For example, hidden within the Southern edge of the Shivering Isles (I'll discuss the actual realm and why we're there shortly) you'll find an ancient abandoned temple. Once you get inside it comes to light that it's been infested with ghosts, all looping through time and repeating their greatest moment of failure again and again as they are overrun by the Knights of Order. Unable to physically touch the ghosts, good or bad, you'll need to find a way to help defend the temple and free the ghosts from the curse.