For what it's worth, those buying for Zombie mode(in order of my preference):
Map Pack 2 - awesome and very challenging, best of the bunch IMO (unfortunately the first few levels are painfully dull) Introduces the Hell Hounds which are great.
Map Pack 3 - Very fun, the addition of the Monkey Bomb is great and the Pack-A-Punch is cool, however this map is pretty easy compared to the other two. Too many choke points where you can just hole-up and last many rounds.
Map Pack 1 - decent, a good introduction to the colas
[quote name='tigerpants']i don't understand why these aren't always priced at $5, seriously, they would sell at least three times as many, which in turn would make a lot more online players have these optional maps, which would probably increase the sales of the games.[/QUOTE]
They sold over 7 million prior to this sale at $10 a pop. $70 million in the bank just for map packs ain't too shabby. I bought them all at $10 and got WAY more than my money's worth out of each of them just for the Zombie map. I've never stepped foot in the standard MP pool. My group of friends enjoy Zombie mode more than L4D.