The entire Trial of a Time Lord season. Confusing, pointless, and with gaping continuity errors, along with the least charismatic Doctor ever (including William Hartnell at his grumpiest).

I adore the Sixth Doctor, but I certainly can't disagree with the point that Trial of a Time Lord was a horrible misfire. I'm always somewhat amazed that the series wasn't cancelled on the spot after The Ultimate Foe.