Best game of 2004? I'm waiting to learn more about Metroid Prime 2 and Wind Waker 2. I'd bank on either one of those.
Biggest letdown? Don't really know. If Devil May Cry 3 is released this year, I'd bet on that.
Biggest surprise? Nintendo's "mystery machine" will be a giant robot octopus that is programmed to seek and destroy Osama Bin Laden, George W. Bush and Bill Gates by any means necessary.