We had a three strikes rule with regard to MASH. Strike 1 - Hunnicutt (Mike Farrell) instead of Trapper John (Wayne Rogers). Hunnicutt was just a lot more boring than Trapper. Strike 2 - Col. Potter (Harry Morgan) instead of Col. Blake (McLean Stevenson). Stevenson was a very funny comedian, and he played off the other actors really, really well. Morgan was fine as Potter, and sort of acted as a moral compass at times. But Stevenson contributed to the anarchy of the early shows. Strike 3 - Winchester (David Ogden Stiers) instead of Frank Burns (Larry Linville). Frank was just a brilliant character - it was hard to top that. Each of these three replacements were fine. The actors were good and so forth. But each made things a little more staid and a little more conventional. Also, when Wayne Rogers left, it made Alan Alda the sole star. And Alda definitely pushed the show into his own direction over time. In all of these cases, I think part of things simply reflected on the tone and writing of the show. As the show aged, the show lost its edge. There were often moments of brilliance, but they were fewer and further in between.