I'm not a good person to base this one as I haven't really played CoD online since 2,3,4, and w.e the one after that was, but I'm personally just looking forward to the WWI Battlefield game and I have friends who are also eagerly waiting for it. It's not a war that seems designed for a game like this (trench warfare that is), but from what I've seen it looks very cool.
There's an opportunity there for a great campaign in single player as well... I hope they have something akin to All's Quiet on the Western Front. It's a war that's generally been overshadowed by WWII.