Instead of the nuke being a 25 killstreak, now after you kill one person, they drop an item for you to pick up. That item then gives you an objective (like kill two people, or kill one person while crouched). Then you get a nuke. Oh, but it doesn't end the game. So you'll probably be seeing multiple nukes per game.
This alone makes me unsure about buying Ghosts.
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If I remember correctly from the reveal yesterday, they said that fulfilling the objective gives you a care package. Said package only has a CHANCE to get the ODIN Strike. It won't get it every time.