Some critics were alarmed by what they felt was Mann's reluctance to have a feeling for human relationships –we are in the country of stoic individuals conducting themselves by codes of honor and conduct that places weight on the action, not words and their adjectives--the movie is about human relationships reduced to the occupations that command everything; emotional attachments are a luxury the characters, cops and crooks alike, cannot afford. This is a given in heist dramas, but tiny, really, has been done to show the devastation that The Life has on the personal level. Pacino has grudgingly accepted the isolation his work has forced him into and pursues DeNiro without let up, whatever the cost to himself or those around him. DeNiro's character, in turn, has a code that says, in effect, that someone in the life needs to be ready, always, to abandon whoever and whatever is around them the minute they know the "heat" is around the corner; the tragedy is slowly set into motion as he violates his own code, his rules for existing in the life he's chosen and attempts to take his girlfriend with him. His end is inevitable. For me, Heat's success is how Mann expands the minimalist conventions of the narrative line and examines the irrevocable ruin in human relations that the characters' choices result in.
I don't know about the characters being unrealized since I think this is in the tradition of Hemingway wherein blatant introspection is nil. Still, much is conveyed through a series of small details, glances, scars. Perhaps you don't see it, but there's a lot that is said between the lines here, and the acting--Jon Voight is particularly effective here with his restraint, among others--creates a tangible feeling of emotional attachment being hammered into silence by a rough trade. The bit with Pacino's daughter is the least convincing thing in the film; my impression is that Mann had four to five hours of film he had to edit to an hour. This is obviously a truncated storyline that should have been excised from the film. But it's a flaw I can live with. Mann has been taken to task for not making his case about alienation by subtler means, without resorting, as one critic wrote, "….to extremism because the vast majority of people never get so mesmerized by their jobs that they lose their humanity the way De Niro does." The complaint, of course, is that Mann loves the build-up to a grand explosion of feeling where only a character's capacity for ballistic reaction can satisfy the need. Mann, though, I think is well in the tradition of dramatic tragedy, as DeNiro's character's, master thief, thorough professional, a planner who makes no mistakes in his agendas, assumes that he can defy the odds against getting caught and thus assumes his carefully articulated professionalism will shield him from unlucky happenstance. He is a sufferer of unwarranted pride, a carrier of hubris who claims credit for all that great around him. The tragic form demands that the Universe correct itself; since one thing corresponds with everything else within the dramatic frame, equilibrium must be reestablished.
Heat is a tragedy, and tragedies require extremism. There is no more extremism here than you'd find in Shakespeare. This isn't saying that Mann's work here equals The Bards, but only that the outsized action we witness is in perfect scale with the tragic form. It operates at the appropriate level. Heat is a movie, and movies generally demand "extremism." Films are required to be "larger than life," perhaps, but "extremism" here is a general requirement of both tragedy and the noir aspects Mann is working in. The conventions of the narrative style don't allow for the middle ground, the kind of emotional richness reserved for the world's civilians, with straight jobs that have regular hours. The minimal and the maximal are the options in this case, and Mann does what I think is a credible job of getting something operatic from this story of two men, bereft of other human satisfaction and nuance, plunge ahead to an inescapably lousy ending. The scale of the Heat works beautifully.
The Wire, as I said, is one of the best television dramas ever, period. It comes from writer/producer David Simon. His book Homicide: A Year on the Killing Streets inspired the edgy, quirk-ridden genius of the late Homicide: Life in the Street, produced by Tom Fontana and Barry Levinson. Simon has a genius for getting the stories of all involved just right. Under his direction, he creates complexity, grey areas and flaws, and other gripping nuances in characters that make his unique style of crime fiction fascinating, arresting, and moving. The distinction between The Wire and Heat, as you've alluded to, is the difference between TV and movies as forms; a continuing weekly drama can develop characters over time, and layers can be added without straining credulity. Movies, even long ones, have to be more efficient in how their characters and plot mechanisms are deployed. In any event, I think both projects are fantastic pieces of work.
I have an affection for some films that have intractable flaws, along with the works of odd and flawed novels and messily writing poems. There is much I find to like and admire in Apocalypse Now and Heat, enough, indeed, to make them worth initial and subsequent viewings. A good deal of what these two long and notable films deal with is an idea of a character's humanity getting wrapped around a Big Idea, whether it's seduction with origins ideological or professional. The drama, which I do believe is convincingly put across as a felt experience in both these films, comes as characters find themselves making decisions to finish the tasks and duties they've set for themselves, no matter how profound their regret and misgivings are. Style, of course, has much to do with how watchable these outsized actions are, and both Coppola and Mann managed watchable movies that caught, manipulated, and sustained their respective tones. Heaven's Gate, though, I found singularly unwatchable, the problem is that Michael Cimino isn't a particularly interesting chronicler of people's lives as they move toward their destinies. Vincent Canby called worse than a forced tour of your own living room, and I'm not one to argue. The Deer Hunter, in turn, was pretentious, vague, structurally incoherent from the get-go. This aggravating movie was like someone continually clearing their throat to make an Important Statement but never delivers anything the least bit edifying.
Getting human beings as "they actually are" is a conceit and is an impossible task. Characters in narratives, regardless of genre, are all ideal types. The question really needs to be whether you appreciate a particular director or writer's creations in a terrain more or less created out of whole cloth. Different genres have different givens as to what sorts of nuances and backgrounds characters have; this leads us to stereotypes, of course, and what we respond to is how well someone might avoid the obvious and give us new wrinkles, twists, turns, and habits of mind. David Simon is terrific at this. Mann, in turn, has his moments too.