The show definitely felt different and just wasn't the same once John left. The original OHP when it was launched was truly that - a live party, broadcast from John's own basement with live callers, on-air requests, guests and the like. All of that is difficult to re-create, especially since the show has not been truly "live", but has been voice tracked for some time. Keep in mind as well that the first OHP was broadcast in the late 1980s. As
@radiorobert alluded to, that was a very different time for radio in many respects as both a business, the amount of listeners to OTA broadcasts and the lack of a lot of competition for radio listeners' attention that has come along since.
Of course, as most everyone here who's been or is still in the business can attest, listener tastes and preferences also change over time. Lots of popular DJs, VJs and nationally syndicated programs that were wildly popular in the past few decades, fizzled out or are no longer with us for whatever reason.