These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Base Breaker: Rise of the Lycans. Some fans hated the film as, due to its nature as a prequel, the story shifted away from that of the romance between Selene and Michael. Some fans enjoyed the film precisely because of this.
Designated Hero: Selene is only "good" in the sense she is the protagonist. She's never particularly "nice" to anyone except Michael (once she falls for him), does not respect humans or non-soldier vampires, and does not hide any of this. And in Awakening, she brutally slaughters humans out of hand despite being able to disarm, evade and incapacitate them at will.
Said humans are always actively trying to kill her, and are systematically exterminating her species. Plus, most of them turn out to be Lycans. She also is somewhat friendly with Detective Sebastian.
Genius Bonus: The Corvinus clan, the original patriarchs of the Vampire race, are named after the 15th century Hungarian king Matthias Corvinus. If you know your vampire lore better than most, you might know that Matthias Corvinus was a contemporary and political rival of Vlad Tepes, the historical figure that Stoker's Count Dracula was based on and named after. note Vlad's patronymic title was "Vlad Dracula" ("Vlad, Son of the Dragon") as his father styled himself "Vlad Dracul" ("Vlad the Dragon"). Naming the founder of the Vampire race "Corvinus" is a subtle Shout-Out to the most famous vampire in all of fiction.
Moment of Awesome - When Viktor heads off to kill the 'Abomination', Michael, the newly transformed hybrid emerges, and as Viktor and he stare each other down, Michael SHOVES Viktor, sending him flying back.
Moral Event Horizon: Viktor allowing his own daughter to be murdered for consorting with Lucian in the third film. It's so monstrous, nobody that has seen any other film will be able to know whether to root for the vampires or the Lycans after that.
What the villains in Awakening planned to do to Eve.
Shown earlier, in Rise of the Lycans, during the outbreak of the Lycan slaves. Where some of those rather large ballista bolts landed could be a little on the squick side for some.
Strangled by the Red String: There is never any indication that Selene feels any real emotion toward Michael; they don't actually have any sort of conversation with each other about anything apart from vampires and werewolves, and they have known each other for a total of about two days. Word of God says this was the way it was supposed to be; special Features on the DVD reveal that the two characters were not supposed to actually be "in love," but rather attracted to each other based on lust, confused feelings, and being forced together.
Special Effects Failure: The first three films have decent CG mixed with animatronics. The fourth on the other hand... To put it lightly, looks like a PS3 game.
Tear Jerker: The death of Sonja is surprisingly touching.
Lucian's retelling of Sonja's death to Michael is also very sad, and really makes you feel for the guy.
They Wasted a Perfectly Good Plot: Not only is Lucian not actually dead when Raze finds him during the climax of the first movie, Raze is carrying the blood samples from Amelia and Lucian has already been injected with Michael's blood. This troper is greatly saddened to have missed the chance to see a Hybrid Lucian fighting Viktor.
Too Dumb to Live: Both vampires and Lycans in Awakening. "Humans now know we exist, want to kill all of us off, have gotten pretty close to successfully doing so...so, instead of forming some kind of common cause, let's continue fighting each other. ???
This is probably Justified, as Antigen, which has at least some connection to the Purge, is secretly directed by Lycans.
The Woobie: Lucian, at the end of Rise of the Lycans.