I watched the Epilogue on YouTube. I'm satisfied, and I saved myself $10.
I don't think that the ending contradicts what the Prince had been trying to accomplish.
Cleansing the land was Elika's quest, not the Prince's. By the end of the game, the Prince is playing the role of Han Solo - he's in this for love, not because he hates the bad guy. Prince's quest is Elika, and when she dies, he feels as if he has lost. That's why he revives her.
I thought it was pretty masterfully done, and a great example of "games as art", telling a story that is the directors vision.