If not for Nazi Zombies, this game would just be yet another WW2 FPS, but a solid one at that.
Multiplayer has perhaps the best action of any WW2 shooter, mostly because it borrows heavily from COD4. It is really fun to rank up, and some maps are masterpieces, but others are pretty much garbage. However, these are mostly from the map packs, so you don't have the bad ones off the bat. A great counter to these bad maps is the voting system, which allows players in the game lobby to vote to skip a map. Thank god for this feature.
Now for the best part of WAW. Nazi Zombies. This is essentially a survival mode where you fight against increasingly large forces of zombies, using an array of WW2 weaponry. The first map, Nacht Der Untoten, comes with the game. However, if you truly want a zombie expirience, you need to buy the following three map packs. each has a new zombie map, improving upon the last. With these four maps, zombies can appeal to any person's taste, whether it be bare simplicity (nacht Der Untoten), An expirience as thrilling than a horror movie (Verruckt), or purely unrealistic but amazing zombie-blasting (Der Riese), It has everything here for you.