Yeah, he’s right, it doesn’t get any better than the initial four season run. And there are some very ropey patches in the later seasons, though by the end it gets really good again.
The sequence is: four seasons on Fox (but aired originally as five), cancelled. Season five is four “movies” aired as 16 episodes on Comedy Central. Then four more half-seasons aired on Comedy Central.
The movies are OK, but they really suffer as individual episodes from the format. Season six is kinda bad, though there are some good episodes in there. The attempts to be topical really fall flat. Season seven is mostly great.