Sheridan was a congenital liar, tactically deficient, a braggart, and a true jerk.
But his contributions went beyond battlefield wins and losses.
Bruce Catton, I think, captured it perfectly in A Stillness at Appomattox when talking about how Sheridan relieved Warren at Five Forks: "This was the first time in the history of the Army of the Potomac that a ranking commander had been summarily fired because his men had been put into action tardily and inexpertly. Sheridan had been cruel and unjust--and if that cruel and unjust insistence in driving, aggressive promptness had been the rule in this army from the beginning, the war probably would have been won two years earlier."