Critical Research Failure: The authors get almost nothing right when they make reference to history, frequently ignore both the original novel and most of the film versions when they cite the first book.
Die for Our Ship: Jonathan is killed early in the book, and Mina goes gaga for Dracula. An in-universe example perhaps?
Lost in Imitation: This book is more consistent with film adaptations that the original novel, from vampires burning in sunlight to Mina and Dracula being in love.
Ron the Death Eater: Jonathan gets an absolute hammering in this book, having turned from a decent if slightly bone-headed guy to an alcoholic, abusive whoremonger. Seward gets it to a lesser extent, being a dick who never forgave Arthur for winning Lucy's hand. But the worst is undoubtedly what they've done to Bram Stoker, here a petty, jealous egomaniac who'll step on anyone to stay famous.
What an Idiot!: Van Helsing. His views on Dracula have almost done a complete 180-degree turn between the end of the original novel and the start of this one, but he never apologizes for his error to other characters, nor even admits to it until they've already found out about his omission. When he reveals that he has been turned into a vampire, we get to see his point of view to make it clear that he's still himself and not really trying to hurt his former friends, except maybe for being drunk on power, but everything he does from then on just happens to look like Demonic Possession.