Dead Island: Riptide - Preview @ G4

G4 has a preview for this game. It is based on hands-on time with the game. Some spoilers ahead, so read at your own risk. A quote from the beginning of the preview:

Our demo threw us into about 6-10 hours into the new game as our two-man team lugs around a chain gun to a semi-submerged church out in the middle of the swap. As it turns out, the rains didn’t just bring the original characters to the new island. You’re going to be waist deep in water and the undead. A returning cast of characters means that players of the original title will get a leg up on the rest of the gamers by being able to transfer their characters over.

More information.

The first game hasn't even been out for 12 months!

I would have imagined they'd need more time to make a good sequel.

Is this really a sequel? I assumed it was just a standalone expansion.