Extra Punctuation. With Zero Punctuation, you generally know how it's going to turn out. Yahtzee rants about a game, often blowing a flaw or two out of proportion (although sometimes, it's justified). Often the only thing surprising about Zero Punctuation is when he reviews a game that people weren't expecting.
With Extra Punctuation, you never really know what the topic is going to be. While it's often a sort of add-on to one of his Zero Punctuation reviews, he does bring up some interesting ideas, like how player-given names could be voiced. That, and it does have its humourous moments. Yahtzee's rants in Extra Punctuation tend to give an insight into the... for lack of better term "method behind the madness."