... I just spent an hour writing a review... I was then signed out of GR and lost the entire thing. So here's the basics:
There is no story. Cut scenes are used to move players from one mission to the next, but there is little backstory which does not engage the player.
AI is horribly unbalanced. Allied AI are useless and Enemy AI are either too easy, or are far too difficult as they only target the player, with uncanny accuracy. Veteran Difficulty is far too difficult and makes the game frustratingly hard, not fun and challenging.
The Multiplayer isn't as good as COD4. Tanks ruin the gameplay style, the multiplayer maps are ugly and difficult to navigate. They're also too big or too small and due to the way they're designed, it encourages camping.
The guns are unoriginal as they are ported from COD2 and 3. Although there is the addition of a "red-dot sight" and scopes.
The multiplayer graphics are not as polished as COD4.
Although the single-player campaign is seriously lacking, the 4-player online co-op is a nice addition.
Zombie mode is FUN, but is repetitive and will quickly lose it's appeal.
In the end COD:WaW is a step backwards. It's Call of Duty 3 x 2 and lacks the charm of COD4.
It's worth renting, but given the choice again, I wouldn't buy it. If you have COD4, stick with that and hope for a new map-pack rather than investing 65$ in a game which isn't worth the money.