Like so many shows, TOS seems to have started as an ensemble type production. Perhaps because the writers were exploring new characters and situations? By season 2, the Big Three had been established and really it was the big 2 with Kirk and Spock in a death match for supremacy. By season 3, the air had gone out of the balloon, everybody knew the show wasn't being renewed, Nimoy was from what I gathered drinking himself into oblivion, Fred Freiberger was feeling his way along (unlike some fans I don't see him as incompetent or stupid) with some hits and some misses. Boredom, ego insecurities and perhaps a genuine feeling that the only way to liven up dreck like "Spock's Brain" and "and the Children Shall Lead", etc...was to go over the top. I think the combination of a new show runner and rotating directors really meant there was a power vacuum for him to work in. I have occasional bouts of mild tinnitus and I can understand how awful it could be, but I really doubt if that's any more than a contributory cause of the acting style. If you can find a copy of the 1970 TV production of the "Andersonville Trial", you can see him doing some outstanding work under the direction of George C. Scott. Also he was playing off an incredibly talented cast of actors including Richard Basehart and Jack Cassidy who obviously were delighted to be able to get away from the drudgery of weekly series work and sink their teeth into something a lot meatier. It would be easy to just say Shatner's ego got totally out of control and blame it all on that, but I just can't see it as being that simple.