I really do not get the complaints. World at War is a good game and Treyarch are good developers. End of story. It doesn't do anything all that new and in many ways it's similar to Call of Duty 4 but with some new (better) graphics, but for what it does do, you really can't complain. As far as single-player is concerned, it beats the shit out of Call of Duty 2, that's for sure. The story itself more or less sucks, but frankly the story also sucked in every single game up to Modern Warfare (and even that doesn't have a great story so much as it does have a slick presentation of it).
Some people are making complaints against Call of Duty 3, and to those I simply respond with: they had eight months to make that game. I think that such an accomplishment deserves a "holy shit", even if the game is not really phenomenal.
I mean, what the hell, it's just a bunch of stupid shooter games. They've all been nearly identical since the first came out, and have received mostly minor changes and upgrades outside of the graphics. Modern Warfare 2 isn't going to be some huge revolution in gaming, but rather it will play to the strengths of the first one: glitzy, big-budget presentation, plus fast and focused gameplay.
With all that said, if they're moving to Vietnam, then I'm interested. If Treyarch can pull off a real sense of tension and atmosphere then they might be the first developer to make a game that really does justice to the war.