My no spoilers rule does make this a difficult post.
In Changeless, Gail Carriger expands and adds detail to the alternate Victorian world she debuted in Soulless. It's a vivid paranormal world and Changeless beefs up the steampunk elements.
There are other differences between the original and the sequel. In my opinion (in other words--I could well be about to say something stupid) Soulless exploited the conventions of Regency romances to good effect. As a Regency reader I was on familiar ground despite the original paranormal twist Carriger added to her Victorian world.
In Changeless, the Regency conventions (and I'd argue, the romance) are gone. The sequel is an Adventure. Read and enjoy.