Were it not set in the gay underworld of its era, 1980's Cruising would be a largely unremarkable film. But provocateur William Friedkin did set it in this underworld -- a seedy, sex-filled shocker than must have had audiences in tears -- and thus it has become a cult classic, almost notorious, really.
The story is, by and large, traditional serial killer fare: Someone is stabbing gay men to death, often in lewd situations. The NYPD captain (Paul Sorvino) sends in Steve Burns (Al Pacino) undercover to ferret out the killer. The straight-edge Steve learns all about gay culture, in which pocket to put bandanas to indicate your proclivities, and so on. But by and large he's just supposed to "go out there and find the killer." But the undercover activity takes its toll on his psyche, most notably in his (non-gay) relationship with Nancy (Karen Allen, virtually the only woman in the film at all).
In the end, the mystery will be revealed... maybe... and that's what frustrates so many people about the film. The ending is interpretable in at least three different ways, and that may get you talking about it, but it's unlikely anything will be resolved by it.
As with so many films, Pacino is the reason to watch the movie, there's no doubt about that. His performance is unforced and genuinely conflicted, even in scenes where he is asked to be slapped around (still undercover, mind you) during a police interrogation by a large black man in a jock strap and cowboy hat. No, you read that right. Friedkin is messing with you throughout this movie. He even messed with the actors: Karen Allen reportedly was only given pages of the scenes she was in, since she wasn't supposed to be aware of her boyfriend's undercover activities. Imagine when she saw the finished product...
Amazingly, Cruising is still unsettling even after far more explicit fare has been produced in recent years, and that's a testament to Friedkin's power to make you feel out of place through lurid camera angles and creepy lighting. It doesn't hurt to have so many people getting brutally stabbed to death, either. Friedkin's first cut was reportedly outright rejected by the MPAA.
Cruising may be more interesting as a film to argue (or complain) about than it is on its artistic merits, but it's still worth seeking out and seeing at least once... if only so you can have an opinion about whodunit yourself.
Friedkin offers a commentary track (expect little) along with a lengthy making-of featurette on the DVD release.