Man you guys are missing out. I hate zombies, and everyones infatuation with them in general but can't get enough of Nazi zombies.
First you must have at least 3 people if not 4, otherwise you won't last long and it's not as fun. Teamwork is ESSENTIAL.
As irratebass said, it's all about earning points to open up the next area. There is a weapon box where you can buy a random weapon. There are some kick ass weapons in the box that you'll never find on the walls. After you "pull" from the box so many times it disappears and reappears elsewhere on the map. You have to track it down to keep getting the good shit. Most of the time the room where the box spawns has a trap you can turn on to help defend the area. Those traps need electricity to work, which means you have to open a certain area to get to the breaker box.
Second, there are also colas that add to your play. Stuff that makes you reload faster, revive others quicker, and makes you stronger(so you can take more hits before dying). These vending machines are spread out and the cola is expensive so you have to play smart when spending money to open doors and what guns/colas to buy. You also lose your cola if you go down.
Third, in the final map released for WaW there was a weapon "jukebox" that you could upgrade any weapon you are carrying to give it additional bonuses like damage, fire rate, max clip size, etc. I'm not sure if this made a return to Black Ops, as I haven't seen it on the first map.
The mode is pretty complex and the maps are pretty well designed, so if you aren't surviving long enough to open multiple rooms, power things on, find the weapon box, etc. you aren't really getting a true feel for the game.
My group of friends play to see how many waves we make it, as going for score isn't really suited for teamwork. The best we did last night was Wave 9. By comparison, in WaW we were going for 35-45 waves. The higher the wave, the greater number of zombies and the stronger they are, so once you get to around 20 things start getting really tough.
Long post summed up short, don't give up based on an early impression, it's a pretty deep and involved mode that really shines with 4 players.