Of course he can! He has! I could name several, but my reason for joining this site was because of the Fallout 3 review. C'mon, folks. It was as close to Branston's Pickles as he's ever got! Maybe no special chunks in HIS eyes, but I liked the game and he seemed to enjoy it himself.
Let me clarify something here, though.
Yahtzee will always put a game through the wringer, regardless of how good it was, or how squeeky-clean the company that made it is. It just happens, and it's funny as hell. Any review that he speaks of being delighted by it without a dreadful BUT followed by a diatribe of suckiness can probably be described as good, and he had those. You're not gonna find him sucking on the tits of wobbly optimism because of a game.