I watched the first Underworld very recently, and it didn't take me much time to watch the first sequel.The first film was not a critical success, but I liked it anyway. Evolution was even less successful with critics but I figured it would be good enough. The end of the first movie made it clear that this one would be about Selene going up against the last vampire elder.
The movie begins with a backstory that's set many centuries ago. It shows that Marcus Corvinus had a brother that was the first werewolf to ever live. Despite being a vampire, he tries to convince the other vampires to spare his brother. However his werewolf brother is too dangerous and can't control his own power. Which makes it hard for the others to show him mercy.
In the present-day Selene is no longer a friend to the majority of vampires. She killed Viktor, and the last vampire elder Marcus wakes from his slumber. When he realizes what happens, he goes after Selene and the vampire-werewolf hybrid Michael Corvin. While Viktor was one of the most feared vampires to ever live, Marcus was even stronger.
I ended up liking Evolution a little more than the original. I thought the new parts of the story were interesting enough, and I liked the battles a lot more than the original. If you weren't a fan of the first film, the sequel will not change your mind though. I still have a few more sequels to see, but I still consider myself a fan of the series.