James Cagney is no stranger to playing a criminal, and usually is best identified by his many roles as various criminals. I will say I am not all that schooled in the matter of Cagney as a criminal, and I have only seen a few of his performances. His performance in Angels here is quite different from his later criminal performance in White Heat. In White Heat he is quite impressive as a just about pure evil psychopath, but here as Rocky he is not a completely hardened criminal. Cagney is decisive as many of the popular actors of this period are because of his distinct voice, and acting style. I will say that Cagney's style neither annoys me, but I don't exactly find it riveting. In this particular film though, I will say it works pretty effectively for Rocky. Rocky in many ways is a standard gangster trying to deal with back stabbing head gangster, and Cagney's style does work well for a rough charismatic and energetic gangster like Rocky.
Cagney's whole movement, and tough command make Rocky a believable character, and I do not doubt his ability to do what Rocky does. This is standard gangster from Cagney in these scenes. This is not something I think should be overlooked though, or underwritten. Cagney was the only person who could play Rocky exactly like this, and he handles these scenes properly and effectively enough. I think he is particularly effective at showing that killer edge of Rocky in the shoot out scenes. Although this portion of his performance is good, but I think the best part of his performance is Rocky's relationship with his old friend Father Connolly. This allows Cagney to show more of Rocky than just a rough gangster side of Rocky. He and Pat O'Brien create an honest friendship between their two characters. Cagney subtly shows a small little soft spot Rocky still has with for his old friend, even with their small conflicts. I like how he shows an honest love for his friend that is deep within his harsh exterior.
I enjoyed Cagney's performance up until just before the end of the film. I felt he showed an effective portrait of a rough criminal, but also strangely heartwarming in his friendship with the priest. In fact his warm friendship with the priest showed an actual heart in Rocky without at all forcing it, or undermining the rest of the character. It is this heart that made me honestly sad, and sorry for him when Rocky (spoiler) is sentenced to death. Cagney though does top his performance in his final scene where he possibly "turns yellow" at the electric chair. He is chilling because he honestly sounds like a real man who is pleading for his life, an amazing end to a strong performance.