IMHO, GoW2 is far better than GoW1 in almost every aspect.
With that being said, the drop-in drop out aspect of the multiplayer campaign was better in GoW1. I do not know why they removed it. Halo 3 campaign was great with 4 player multiplayer, but there is no matchmaking and one can only play with invited people. In GoW2, you join people randomly but do not know who. As long as they have some sort of matchmaking (ie, search screen) and one can join in progress, the campaign in GoW 3 will rock especially if it is 4 player.
Going back and forth from GoW1 to GoW2, host advantage is extremely annoying in GoW1. The fact that one could pick and choose which game/map in GoW1 was nice. With that being said, so many times the host would shut down the room once he or his team was loosing. There were so many glitches in GoW (running and shot gun blasting for example), that it became extremely unfun. In GoW2, matchmaking is a bit better, and they have taken a Halo type approach with the map selection etc.
I agree with the comment about GoW 1 being more raw. Its kinda like GoW1 = terminator, and GoW2 = terminator 2. As long as GoW3 no equal to terminator 3 (except for Kristinna Loken, now she was pretty hot), I think the GoW finnalle should be pretty good.
Xbox and PS3 Gamertag = Xerostomia
Wii = I'm too lazy to get the number