I'm sticking with Battlefield 1942 - there's no chance that will win, most people here never played that, but as much as I love Metroid Prime and Wind Waker, this was something very different and new, in a spectacular package.
Well, as I said, at least on mainstream level new - WWII Online launched a year before and it was online subscription based virtual WWII battleground (with map that is 1:2 scale of West Europe - you could see columns of hundred tanks rolling toward some town), but that is as niche as it gets.