I don't think ZP has gone downhill at all. I just think people are bringing unrealistic ideals to the videos. Face it, he is a critic. He claims he's a critic. He criticizes games. That's his job. He doesn't review them so much as he criticizes what he doesn't like. Now, that being said, he does, in the process of taking a dump on a game, discuss game play issues, character development, plot and lack thereof, and all of the other niceties for which we look in a game.
The biggest problem, I believe, are the fans of the series. He's putting out the same level of humor he has in the past. The fans have just grown bored. Short attention spans anyone?