I was thinking it was a bad idea to be it myself, but I did anyway. After playing it for quite a while I can say that it IS actually worth the money, unlike first strike.
I believe it is worth the money because i play zombies more then i play multiplayer and the zombie map alone i think personally is worth 15 dollers cause the map is huge, new perks, george is on there, new cast, hard as hell acheivments, and a constantly moving pack-a-punch machine.
Thats actually the only reason why I got the map back was because of zombies. Me and my friends played it for three straight hours hella fun. Though George is a real ball buster. Heck I haven't even played the online maps yet since it was that fun man. Go ahead its crazy fun dude its worth every penny if you got friends to do zombies with.