I’ve now played through and beaten every Halo game except ODST (which I’m sure I’ll get around to someday). Halo 4 came out just last month, and represents something of a new direction for the franchise as it begins to explore the “Ancient Aliens” origin of the Halo megastructures. It also begins to (finally!) develop the characters of the franchise’s hero, the Master Chief, and his artificial intelligence-based guide and love interest, Cortana.
I’m not going to pretend that the Master Chief is some sort of deep, memorable character. He’s basically just the most prominent iteration of the Doomguy, only less expressive since you can never see his face. But nonetheless I’ve had an affinity for the Chief since playing through the first Halo.