Well, I'm not sure he underperformed given that he did kill 5 hookers while at SMU. He would definitely be in the running for most over-sized ego though.
Other than the sound-bite stuff, which you can usually catch any candidate doing, what disappointed me the most about Perry was his goofy little showdown with Romney over the undocumented groundskeepers or whatever. The intensity in his face just showed a blind combativeness, personal unpleasance and strategic laziness on his part. I know a lot of the other liberal Texans who have been scrutinizing his governorship aren't surprised or unhappy about it, but really did expect more from someone with 20-some-odd years of state-level executive and administrative experience; where I assumed national party talking points and voting factions mattered a lot less, and that at the state level you actually had to do real work.