Count Dracula is depicted with very hairy palms in his first appearance- this is a typical part of the vampire myth, but it's also part of another myth... Now, he has some very attractive wives but he's obviously still very much in love with Elisabeta... Could Dracula have started both classic myths in one fell swoop by being locked away in his castle, with his true love gone forever, for half a millenium? Stories about him would certainly spread in that time.
There's a sequence in the film where Mina chucks pages from her diary overboard into the ocean, with a voice-over reading off text that is not in the novel ("Perhaps, though I try to be good, I am bad," etc). This could be an in-joke/explanation of why the romance story isn't in the book: Mina destroyed all the written evidence!
Count Dracula's bizarre behavior during his time with Jonathan is very likely explainable by the fact he really hasn't dealt with regular humans in centuries (save his Romani mercenaries). Obviously, he has a little time to practice before he starts his seduction of Mina. It's also possible he observed Lucy's suitors, Jonathan, and others for a sense of "okay, how *DO* people interact nowadays?"
Mina's cheating in this version of the story are more understandable with the fact the movie plays up Mina being sexually frustrated and Jonathan a boring wet blanket.
Also, she appears to really be the reincarnation of Dracula's lost love.
Jonathan is able to recognise Dracula in his younger form. When he had first visited the castle, he saw a portrait of the younger Dracula and assumed it was an ancestor.
Dracula having his brides feed on Jonathan but not kill him. Technically that means he's cheated on Mina, making the count feel okay about making a move now.
Mina beheading Dracula at the end is not an act of love, but one of rage and vengeance: she's free from his mental influence at last, and remembers that he raped and murdered her best friend, and permanently traumatized her husband.
Mina's marriage with Jonathan is going to be awkward given the ending where she professes her love to the Count.
And almost having sex with him. And holding a loaded rifle to Jonathan while protecting the Count. And actively aiding the Count's escape. And attempting to seduce Van Helsing.
Then again, she was under his spell.
That opening scene with Dracula ends before we see what exactly happens to the priests and guards outside the door. Remember that this is Vlad 'The Impaler' Dracula we're talking about here. Try not to think about what he most likely did to them right after. Especially since, if you look carefully, you can see dessicated impaled corpses down near the chapel centuries later when Jonathan is trying to escape. Yeah...