In terms of the overall structure of the film Pentangeli acts as basically a confused pawn in the whole struggle between Al Pacino's Michael, and Hyman Roth. Gazzo effectively portrays this confusion, as well as simply showing Pentangeli as a man who acts as he needs to, and as the circumstance requires it. Gazzo though always also suggests the long history of Pentangeli in the crime world, a history that developed this particularly attitude he has gained. What Gazzo does so effectively in the role, since he can't call upon Pentangeli's history with Michael, is instead to personify an old school mentality which contrasts against the cold efficiency of Michael's new methods. Gazzo from his first scenes brings real bluster to his performance, making his emotions known in an overt fashion whether it is in frustration from not being able see Michael right away, or his inability to get Michael's hired orchestra to play Italian music. Gazzo's approach is the right one as he shows a man who would've been right out at home with Vito, here with his personal style seems of a past age at odds with the new nature of the family.
In this way Gazzo's performance is an affecting work as a man attempting and failing to attune himself to those playing at a different level from himself. In this way his performance works well as a contrast to the duplicitous work of Lee Strasberg as Roth. Where Strasberg puts on a front Gazzo presents Pentangeli plain as though he knows no other way to really do so. These especially well realized in the subsequent scenes of Michael visiting the two men to discover which of them tried to have him killed. Roth is smooth, and oh so innocent. Gazzo though is terrific in seeming more guilty by being so honest in the moment. Gazzo again shows the difficulty of the man in this game by portraying only an intense disbelief, and confusion in his reactions as he fails to even understand that there is a game to even be played. As the film goes on Gazzo's work realizes the victim of the man as he's used as the pawn essentially for his straight forward ways. In the last act of the film a series of circumstances leave Pentangeli as an informant, only really due to his life being threatened than a real vendetta. Gazzo continues to present so well that old school attitude in this creating a real discomfort in the idea of both testifying and being stuck to live out his days on old army base. A remarkable moment from Gazzo's performance comes at the only genuinely duplicitous moment for Pentangeli when he testifies falsely that he knows nothing about Michael's criminal organization. Gazzo's great here that even this is overly colorful in his deflection again as this is not Pentangeli's way, and the whole act seems as fake as it is. This is in stark contrast to a single reaction of Gazzo's when he sees that his brother from Italy is with Michael, in that reaction Gazzo powerfully realizes all that this means to the man with it barely even needing to be said. What's interesting is the one time Gazzo brings a real confidence to the character is at the very end of the film, where he's left with almost no options, however it is when describing antiquity specifically the act of a Roman conspirator getting the chance to commit suicide to save his family and his property. Gazzo brings such a warmth and pride in his delivery of this speech showing the sad state of the man most comfortable with the ways of the past, only seemingly at home when deciding the way of his demise. Although I would I still would have preferred to see the return of Clemenza, Gazzo work fills in that gap beautifully by finding his own tragedy within this aspect story, different than what it would've been however still powerful.