Unlocks. It's the most pathetic addition to Halo in a long time. The loadout system is a good second.
Maybe to someone who does not like unlocks, but I don't mind them and I admit I keeps me playing COD longer than I probably would, because when I unlock most perks and attachments for the weapons I like I end up playing it less and eventually selling the game to due to the redundant nature of the game.
343i are just being smart, they want people to play for longer, and now Halo 4 will have a lot of weapons which means some can be unlocked, big deal. And then you have Spartan Ops (which despite the name shouldn't be compared to Spec Ops, crap name though)
However unlocks are not COD specific, COD just happens to be the most popular and more popularly hated (with good reason, unlocks
not being one of them)