I really enjoyed the original Dead Island, it provided a real feeling of surviving a zombie apocalypse and thankfully was still fun playing alone. The next game in the series is a direct continuation of the first game, sounds like it is set on a different island.
The trailer tries to evoke the feelings of the acclaimed trailer for Dead Island but I think fails. Still, not bad and least has zombies in it. Originally Riptide was planned as a stand alone expansion rather than a new game in its own right.