Warthog run ended with tactical nuke finale.
A non-cliche ending would be, say, achieving a tangible objective that is NOT killing the ultimate enemy or blowing up the facility you've been playing on. Say the goal of the game is to get a distress beacon out. Ending would be having the courier ship slip away while you hold the badguys off. Halo: Reach had this type of ending. There was no boss, there was no big boom.