Yahtzee sounded like his normal, cynical, game-reviewing self when he was on Unskippable. It broke the flow of things quite a bit...His voice, especially. It was like him saying, 'Hey, I'm Yahtzee and I will make no effort to try to adapt to your production.'
Graham: Why are they doing blah blah blah?
Paul: Well, technically, they're doing blah blah blah, so blah.
Yahtzee: Well, blah blah blah SHUT UP!
Didn't like that episode, specifically because Yahtzee was one of the people commenting on it.
On the other hand, Graham didn't do badly in his brief time in Zero Punctuation- he did pull off the fast talking quite well, and it was a solid performance.
I guess Yahtzee is really only compatible with his own show, which stands to reason.