How I felt about it. A standard coming of age film is made edgy by the presence of abusive, tough-love stepdad Robert De Niro. He knows what he wants, doesn't care whether it is what others want, and is certain that his way is right.
De Niro's role as a menacing, cagey family man suits him perfectly. DiCaprio's banner days were yet ahead, but in this early role, he shows the promise later delivered in The Basketball Diaries (and, from a box office point of view, Titanic).
This Boy's Life is a test of wills between DiCaprio and De Niro. DiCaprio always has the sympathy of the audience, but De Niro scores points too. He's right that the kid has been raised too permissively, and that he's on the verge of securing a criminal record. He's been abandoned by his real father, who is allegedly well-to-do. He shouldn't dream of opportunities missed, or blame his mother for her failures.
But while De Niro is right about surprisingly many things, he certainly can be wrong, too. He needs to be in control, and he stays in control by making others fear him. In other words, he's a bully.
But De Niro doesn't see it that way. Instead, for him, there is a narrow way to do things, and people who have trouble following the path need correcting. The method to correct is similar to spanking a child. You tell the person what they did wrong, while you apply verbal (or, if necessary, physical) punishment.
The problem is, De Niro takes pleasure in intimidating his family, especially DiCaprio. He knows his stepson hates him. This pleases him, perhaps because he hated his own dad and actually believes that's how it ought to be. It's part of growing up, learning to hate within specific bounds.
In any event, De Niro plays a more interesting character than DiCaprio. Part of this has to do with the script. He gets excited about a rifle, as if he were still a child, and is eager to be a Boy Scout until he sees his hand-me-down uniform. He wants to hang with his hoodlum friends, yet also pal with a known homosexual classmate. These character traits aren't consistent. He should be sullen, clever, and deceitful. The wide-eyed pretty boy stuff should be banished.
The curious thing is how normal De Niro's kids are. They are nearly oblivious to their father's severe character flaws, perhaps because they have lived with them all their lives, and never try to challenge his authority. A wise decision, at least for them.