I was very sad to see Johnny go. His mix of interviews, skits, comedy and music worked very well. What I loved best was his classy interview style. I don't recall any guests acting as if they were being attacked. Classy, funny and entertaining... A hard combination to beat. Watched him every night since I was a kid.
Contrast this to Jay, who did a very good job. He did not do as many original skits, and sometimes carried on a "feature" way too long. I watched him when I had free time thanks to Tivo. He was not always kind to his guests. In her last appearance, Sandra Bullock had the occasion to say to Jay "You're such an ***" as Jay brought up embarrassing parts of her career. That would not have happened with Johny.
Jimmy... he's a bit more like Johnny. His interview style is more subdued and respectful, though he sometimes gets very animated. I've enjoyed his show too (thanks again, TiVo) and hope he gets the kind of writers that can combine the best of the Leno show with his style.
Daniel