OMG I love Lizzie; I'm so glad I'm finally to this arc, which shows why and how she is the way she is and why she hid part of herself from Ciel.
While the Titanic-esque setting is a bit lame, the zombie angle is clever (not on its own: zombies on such a ship, yes; and the twist with Undertaker and how he created them is also made of win). I even enjoyed the Reapers this time (I tend to find them tiresome) with the Reaper on Reaper (and demon, with Sebastian) fight. It's not the biggest surprise ever to discover Undertaker is a Reaper (er, he literally has a scythe), yet the reveal adds to the world in that we learn more about the Reapers.
And, almost as cool as Lizzie is seeing how Ciel and Sebastian first navigated things immediately as and after the contract was made.