Let us face it, in personal charisma & imposing appearance, Gen Kiyani was no match to either Musharraf or to Raheel Shareef. He was however well liked and respected during his first term of office. But 3 things spoiled his image.
No matter which way you look at it, Abbottabad raid by the US and the fact the OBL was found in a garrison town in Pakistan was an insult to Pakistan, to Pakistan army as an institution and particularly to the COAS. Before becoming COAS, Gen Kiyani was head of the ISI. Assuming that he was in fact unaware of OBL presence right under his nose, indicates his lack of competency as Pakistan’s intelligence chief.
Secondly, he should have retired after his first term, accepting textension of his term of office is indicative of a greedy streak, thus a weakness of character.
http://www.nytimes.com/2011/06/16/world/asia/16pakistan.html
Finally, revelation by Maj Gen Athar Abbas that Gen Kiyani feared backlash from the religious lobby and hence he procrastinated about taking the military action against Taliban, makes Gen Kiyani out to be an indecisive general who lacked the guts to tackle the Taliban menace.
Any one of the Corps Commanders / 3- star generals from the fighting branches, is supposed to be capable of heading the Army; promotion to the COAS position being the discretionary choice by the Prime Minister from the list of recommended names. IMO Gen Kiyani was just a run of the mill competent general who got the job because Musharraf liked him.