I'm signing. I had a great time playing through SP. After three nights of playing I beat it on normal, I'll try heroic next. I only have a few bitches about it. After 2 years of ads and trailers all saying "Your gonna fight for the survival of Earth" and "Now the Covenant have found Earth, so you must defend it", I was kinda mad that only around 1/4 of the game is actually on Earth. Sorry but I've had my fill of indoor hallways and spaceships from Halo 1. I want huge outdoor maps, like the earth levels of halo 2, to be most of the game, I don't wanna go back to another goddamn Ring.(yes I know, even though you saving earth by going there...)
Anyways, Halo 2 definitly does have some shortcomings that i did not expect to be in a game 3 years in the making, but overall, its still a great game, well worth the money.
As for MP, to me it has all the great things halo 1 has, plus some new features that are awsome. I love it. Been playing 4 man splitscreen games for a couple of days now and i have nothing but positive things to say. Man, I gotta get a live account...