So SU&SD recently released a rather scathing review of Cards Against Humanity. You've probably seen it, and if you haven't, I urge you to read it. Because I'm about to vehemently disagree with it, and it's probably best you read it for yourself first before I do, so you can make up your own mind.
Firstly, I do have to concede, most of their criticisms of the actual game are fair. The mechanics of the game are certainly not why people play it. And it's not always funny. And it's frequently just random.