I'm surprised no one has started a thread on this.
This used to be THE late night show for me growing up (when I was lucky to stay up past bedtime, anyway). This show was very influential in showing younger, up-and-coming artists (particularly rap & hip-hop). All the biggest hip-hop artists at the time (MC Lyte, KRS-One, Wu-Tang Clan, Tribe Called Quest) rapping on the last show is one of my favorite TV moments ever.
Looking back now, you notice a lot of things, like how Arsenio sucked as an interviewer and as a comedian. His monologues were really corny to me and he was ill-prepared when talking to his some of his guests (Frank Zappa, for example). He always seemed to struggle with his questions. I think the show started to go downhill when he started to take himself too seriously. Some consider the Louis Farrahkhan episode the death knell for the show.
Despite its flaws, it was still a very influential show for its time.
ETA; There was the show where he gets into an argument wtih Queer Nation about the lack of gay guests on his show (you can watch here). I heard that this was planned. Even if it was planned, I thought his reaction was a little over the top. The audience was really annoying during the argument. I sensed a little homophobia there.