Anyone remember "Gilligan's Island"? It tanked after only half a season and isn't very well remembered, but it's recently been released on DVD.
I think it had great promise as a sitcom, but the casting was horrendous. I mean, Bill Mumy as "Willy Gilligan"? Guy Williams as a millionaire, June Lockhart as his wife, and Marta Kristen as a movie starlet? All three are far too down-home to be comfortable in those roles. I'm not even sure what the rest were supposed to be. And let's not even talk about that clanking metal autopilot.
Although I must admit Jonathan Harris works pretty well as the professor-type.