I like the birthday effect. Children screaming while I kill people is one of my dreams. ^.^ An awesome one would be an inclement weather with different colors of lightning. Like yellow, red, blue, green, and maybe a combination of all of the above.
I don't think you should be able to change the armor in Campaign, but in Multiplayer, they should have more customization abilities than in Reach. They should treat Reach like a customization BETA and add many, many more things in the armory.
The ads for halo are mainly symbolic. It's just telling us that he might GET a jetpack in the game. And it never said how long he was out, so some drifting of the ship is bound to occur. And also, What if the "ship" is just the other side of the planet we saw in H3?
If 343i is in any way intelligent, they would try to move Halo 4 as close to Halo 3 and as far from Reach as possible, otherwise they are going to be majorly flamed. So much that they might want to abandon Halo as well.