Capello was good but predictable and not very tactical.
Allegri on the other hand is super tactical and can adapt and change his tactics depending against which team he's playing, Capello used his 4-4-2 against all teams, long balls to Trezeguet and Zlatan and it worked in Serie A but failed miserably in CL against awful Bremen (thanks to their GK) and (Average Liverpool/Arsenal).
The squad Capello had was one of the strongest Juve squads in the history of the club yet he failed to make the semi's in two years.