A year after Gilligan's Island signed off, Bob Denver was back in a brand new sitcom. That was the good news. The bad news? The Good Guys lasted two seasons, and never made it into syndication.
Denver was cast as cab driver Rufus Butterworth, who used an antique car (customized by George Barris, who also worked on vehicles for Batman) for his business. Not content with that, he and childhood pal Bert Gramus (Herbert Edelman), who owned a diner, were looking to improve themselves. On that point, they were trying to emulate The Honeymooners or The Flintstones. And just like Ralph Kramden & Fred Flinstone before them, Rufus & Bert's schemes never worked in the long term.
Just to remind viewers of Denver's last series, Alan Hale, Jr. was a recurring regular as Big Tom, a trucker. Since I never saw the show, I can't judge whether this was good or bad. The only other alum from Gilligan who had gotten a new series in 1968 was Jim Backus, who was co-starring on Blondie, but that lasted 1 season only. Not sure if any of the other ex-castaways appeared on either show.
So, ultimately, why did The Good Guys fail? Gilligan was too fresh in the viewers' minds to accept Bob Denver as anyone other than Gilligan, especially considering that Dobie Gillis was out of syndication by then. I would've liked to have had a chance to see the show, but, well, I was in kindergarten at the time, and......!
Considering the creative pedigree, perhaps a more appropriate analogy would've been I'm Dickens, He's Fenster, which aired on ABC a few years prior, with Marty Ingels & John Astin. Yeah, that didn't last long, either. We'll leave you with a promo taken from CBS' Fall Preview show for 1968, uploaded by Retro Goop: