Who can forget the scene where Life Sentence kills herself. What makes this more heartbreaking is that she tells Halo that with the war over, she felt her life held no more meaning.
The ending is even worse. After killing Luiz Cannibal and hijacking his ship, and with nowhere left to go but forward, Halo flies toward an uncertain future. Leaving her youth and past behind. Either a downer or bittersweet ending, but that depends on you.