There are two Afflecks in this movie, but don’t worry: only one of them is acting.

In a shameless display of Hollywood nepotism, first-time director Ben Affleck has cast little brother Casey in the lead of “Gone Baby Gone.” The film focuses on the investigation of a little girl’s kidnapping — a highly timely story, given the similar and widely publicized “Madeleine McCann” case. Casey Affleck portrays Patrick Kenzie, a private detective who, upon accepting the job, signs up for a wild ride of dark dealings and deceit that will rock his moral foundations and slowly destroy his relationship with girlfriend Angie Gennaro (Michelle Monaghan). Thankfully, his colorless performance doesn’t spoil a surprisingly successful movie: the good pacing, clever plot twists and engaging character conflicts make up for his forever-frozen expression and laughable attempts at being ghetto.

Considering the central themes, “Gone” deserves kudos for steering clear of being preachy. For a movie exploring the blurry boundary between right and wrong and the problem of what truly defines a moral deed, “Gone” is very sensitive and careful not to pass subjective judgments. The script (also courtesy of the elder, Oscar-winning Affleck) is both thoughtful and thought-provoking without patronizingly lecturing on morality. Always presenting both sides of the argument, but favoring neither, “Gone” leaves the answers to the viewer.

The rhythm and pacing of the movie are well-calculated and consistently good. “Gone” unfolds dynamically yet takes time to explore its characters’ motivations and trace the changes occurring in their relationships with each other. The action scenes offer the right mix of shaky hand-held camera chases and slower, more tension-filled episodes. The plot twists occur at suitable moments, constantly renewing interest in the story line by broadening viewer perspective on characters and events within it.

Considering Michelle Monaghan’s uninspired delivery of a part that should’ve been much better developed — and Morgan Freeman’s insultingly insufficient screen time — it’s up to Ed Harris to save the day as Detective Remy Bressant. Luckily, Harris offers an admirable rendition of a character hardly as one-dimensional and stereotypical as he appears to be initially. His role is crucial both in the plot development and in terms of posing the film’s leading philosophical questions. So it’s reassuring that Harris is competent enough to reveal a character’s complex inner world rocked by paradoxes.

The main problem of this movie, apart from the disappointing acting, is that it sometimes tends to be excessive. Obsessed with realistically presenting the raw urban climate of a ghetto, “Gone” sometimes takes its own street cred too seriously and looks more like a caricature than a faithful representation, most notably in a ridiculous bar scene where every person seems to be a fat, obnoxious, fight-picking punk. Thankfully, once “Gone” picks up momentum, it stops being so concerned with overblown white trashiness.

A thorough knowledge of “Gangsta’s Paradise,” though, isn’t the only subject that Affleck hammers too hard. Moral issues, as open-mindedly as they’re handled, are thrown in the audience’s face one too many times. Yes, we get it: doing the right thing is a tricky business, especially when people seem to disagree as to what the right thing actually is. Spike Lee already told us so, with much less overkill.

But overall, Affleck’s directorial debut is already a step ahead of his disaster-laden acting career. Seems like Ben has finally found the better side of the camera. If only he would stay there. Amen.