Anyone who wasn't impressed with earlier Underworld films likely won’t find much to enjoy here either. Like most entries in this style of movie, it’s best experienced by turning off critical thinking and just letting the show play out. The film isn’t a masterpiece when you consider its story or writing; in fact, the script is occasionally quite poor. There's one scene, for instance, where the Lycans attack the vampires’ stronghold, and the writer apparently thought it was clever to have them simply drive straight into the castle's center and break down the door without any resistance. What…? Overall, the writing feels like a standard Hollywood B-movie production that doesn't offer much substance. If this had been the first film, I doubt there would have ever been a series at all. So why did I enjoy it? Well, even though the script isn’t great, it's not completely awful and provides ninety minutes of entertaining Vampire versus Lycan action. That’s really what it boils down to. Of course, Kate Beckinsale is another reason to appreciate the movie. Seeing her move around in her tight-fitting clothes while she violently dispatches Lycans in imaginative ways helps compensate for some of the script's shortcomings. I might have upset a few feminists there, but I don’t really care about that. The action and CGI are reasonably well executed, which is another reason why I liked it. Thinking about it, Kate Beckinsale, the action sequences, and the CGI were pretty much the main reasons I enjoyed this movie. They could have cast a more compelling villain, though. For most of the film, Marcus felt uninspired and even a bit boring. It’s not the strongest entry in the series, but it doesn't drag the franchise down either. Compared to other movies out there, my enjoyment of this one was above average.

Source on TMDB