Did they drop the ball at the end?
Don't get me wrong, I LOVE the Underworld movies. I own them all, and I read all 4 books. I loved this one too, but I have a few problems with the ending. Maybe this is just me being nit-picky, but whatever.
The way David killed Semira - I wouldn't have a problem with this, except for one thing. Viktor was stabbed through the mouth and out the back of his head by Lucian and survived. The same thing happened to Semira, only from the back, yet she died. If anything, having drunk Selene's blood, her healing should have been stronger. Did David stab higher, and thus cutting through her brain? Did Tanus find Viktor and give him blood to heal that's why he survived, but no one gave any to Semira so she died? I don't know, but they shouldn't have a vampire die from the same injury a weaker vampire with weaker healing abilities survived. Maybe cut her head off instead. And another thing, why was Semira's skin doing that funky color changing thing? Selene's didn't do that when she drank Corvinus' blood. Was the poison still in the blood when she drank it the cause? Maybe that would explain why she died from getting cut through the head.
Killing off Michael - If they really did kill off Michael, I think it was a HUGE mistake. They had so much potential with his character. He was only beginning to realize what he was capable of in the 2nd movie, and could do so much more with him. If they do insist on killing him off though, he deserved so much better than an implied death in a flashback, that was just a total slap in the face for his character, especially with everything they built up with him, as they basically just threw it away. Was it so they could try and push Selene towards David? If so, I think that's a mistake too, as it totally undermines the whole vampire/lycan forbidden love of the first 3 movies, and it decreases the value of the love Selene had for Michael, which gave her a purpose beyond revenge. It's clear that David has feelings for Selene (he said how she's important to him), but she's only seemed to see him as nothing more than a companion (a friend at most).
Marius towards the end - All evidence suggests that he wanted to end the war, not just because of his hatred for vampires, but also so he and Alexia could be together. I also genuinely believed that what he said to Selene was true, that he just wanted her daughter's blood to help him win the war, but wouldn't actually hurt her. Yet towards the end, it seems all that complexion with his character was thrown away and they just made him another hateful villain who was evil for the sake of being evil. He seemed to care nothing for Alexia (did he even know she was dead?), he mercilessly killed Michael, and he taunted Selene with having killed him. It all just seemed so out of character for him based on his behavior throughout the movie until then.
The axed ending (?) - If you don't know what an axed ending means, it's basically a rushed ending that simply ends things and cuts everything off to end it. It felt like once they killed off Marius, they didn't know what to do from there, so they just ended things. Ok, yes I know that in the previous movies they pretty much ended things right after the villain was killed, but they were conclusive endings. In Underworld, Selene killed Viktor and avenged her family, and the lycans, having killed the remaining Death Dealers, all backed off after having seen Selene and Michael's power. The movie then left it open for a sequel with Marcus becoming a hybrid. In Evolution, Marcus and William were defeated, and Selene discovers that she's immune to sunlight. Now she and Michael can be free to be together. In Rise of the Lycans, Lucian and his fellow lycans are freed from slavery and the war begins, but we know what comes afterwards thanks to the other movies. In Awakening, the villains were defeated, and Eve discovers she ca see through her father's eyes too. Selene vows to find Michael and help the vampires to rise again. But at the end of this movie, so much was crammed into less than a minute. After Marius' death, we get a montage explanation for everything that's happening. There's now a chance for peace, Selene is forgiven and becomes a new elder along with David and Lena, the two vampire houses shall unite, the vampires all share Selene's blood (was it hers?), Lena reveals she knows where Eve is, Selene is reunited with Eve. All this happens in less than thirty seconds, either through dialogue or a couple scenes. It was way too much happening at once with no explanation. It's like they just decided to cut it off because they didn't know how to take things from there, so they basically said "this is what happens".
Again, I loved the film, but it felt like they did several things wrong and made several mistakes at the very end there.