Mo Money, Mo Money
If you love Left 4 Dead, buy this thing. This is all I can really say. As someone who does indeed like Left 4 Dead, this was a bit of a disappointment. Considering that the new campaign is only 3 chapters long, I felt a bit cheated. 2 new weapons and 3 chapters that just lead so a more intense version of the ending of Dead Center? Don't get me wrong, it was fun as hell, for a little. After a while I kept on dying, because the ending is so goddamned big that people keep on splitting up, resulting in multiple deaths. Thankfully, the end has tons of supplies scattered around. Regardless; annoying.
The new weapons are cool, but really, nothing special, even if it is fun to tear shit up with the M60. The new atmosphere is cool, but not enough of what it was described to be. Much like Dead Center, it just wasn't enough for me to fully enjoy it. The whole rainy night lit by neon is a great idea, yet I can't remember anything really cool or interesting other than the wedding or the ending. Even the wedding is a bit forgettable... no... no I remember it pretty well. That was pretty funny.
The pack then redeems itself with Mutation mode. The fact that it updates every week is pretty kick ass, and keeps the fun constant and fresh. Downside? How long until you get tired of said mode? It's really up to the user, but I think 4-5 days is enough gameplay time to get enough of a mutation mode. Even 4-5 days is way to much playtime for Left 4 Dead, man.
I'd reconsider spending money for this. It isn't much, and neither is the DLC pack. But for mutation mode, I definitely recommend checking it out. If you really do love this game, go crazy. Steam users have it lucky, dammit.