I watch them every so often, but mainly the one's where I enjoy him making a funny observation or quote.
Super Mario Galaxy: "For me, the interesting relationship is between Mario and Bowser. I mean, on some days they fight to the death in firey climatic showdowns, while on other days they go go-kart racing together, play tennis, even team up in some of the rpgs. Sure he kidnaps the princess a whole bunch, but no one seems to begrudge him for that anymore. It's just what he does. It's like begrudging a dog for licking it's own balls."
Prince of Persia - Retrospective: "It just goes to show, never stick your d*ck in a pudding. It might be still good pudding and you can spend all afternoon explaining that, but nobody's going to eat it because you stuck your d*ck in it!"
Silent Hill 2: "Silent Hill 2 is the game I play now and again to remind myself for all the shiney brown, quick time event, rpg element, space marines, gaming are still worth defending. If I were Batman, Silent Hill 2 would be my murdered parents if you see what I mean."
I could go on and on quoting Yahtzee, but that would take a lot of time. Still, he makes interesting and funny observations. His video series is the main reason I go to the Escapist, with MovieBob being a close second.