This needs to be said. Underworld are good films.
Mind you, I'm only talking about the original trilogy. The other films don't exist for me.
I see a lot of people saying that these films have no story and no moral message, and that they're just an excuse for cool fights. But that's not true.
The films are literally about inequality. You have the wolves living underground, the vampires in their grand mansions. There's slavery with the situation of the Lycans, especially in the third film. There's also a form of this through Selene, molded to essentially be a killing machine by Victor. You can literally see it as a form of brainwashing. Something that lessens as Selene finds her independence. It's also about abuse (especially parental abuse with Victor's character through his relationships with Selene, Sonja, and Lucian). It's almost about eugenics with the whole hybrid aspect that the vampires see as an absolute abomination. Not to mention the revisionist aspect of history we see in the first film.
Underworld is actually about many things interesting when you stop focusing on its dark, action-packed form.
Also, most of the main characters are interesting. Selene, Lucian, and Victor completely carry the three films.
And even though I find Michael "boring," the fact that he's this completely normal, innocent, and kind guy fits perfectly with the story. He had to be like that to be with Selene. It's just a shame the actor really lacks charisma...
I also like how the story forms a perfect loop with the trilogy. It's clear there wasn't supposed to be a sequel.
The story has real narrative coherence.
Also, the fact that the heart of the story is literally the concept of Romeo & Juliet is very appealing. The romance between Lucian and Sonja in particular is quite iconic.
Also, the fact that Selene and Lucian have a lot of parallels. Selene is ultimately a female, vampire version of Lucian, beyond her resemblance to Sonja and her relationship with Victor. Selena is like the perfect mix of Lucian and Sonja, and she will finish and accomplish what they couldn't: kill Victor and go live with their love.
My only real criticisms of these films are (as I've already mentioned) the actor playing Michael. When a character is intentionally written in such a simple way, even if it fits the story, you need an actor who brings charisma to create a real connection with the viewer, and honestly, the actor playing Michael doesn't allow for that, in my opinion. And also the fact that the fight scenes in the first film are very (perhaps too) reminiscent of The Matrix.
Also, I've seen many people complain about how the vampires are portrayed in this film. But I loved seeing a version where the vampires were weaker.