The ending breaks your heart — in it the previously cynical, Ineffectual Loner Prince decides to screw over the whole world and release the Big Bad in order to bring Elika back from the dead. It takes its time to play out, and the Prince, who used to have a smart-assed comment for everything, does not say a single word during it. Plenty of people have called it an Ass Pull or Shocking Swerve ending because it basically means that all the work you've done was for nothing, but if you value the character development, it'll tear you up because it is the only way the game could have ended.
Made worse by the Epilogue. Elika despises him, and leaves him to look for her people.