As the cynics no doubt expected, there are a lot of problem with The Guardian. So, let's address those right up front. First, at nearly 140 minutes, it's way too long, a flaw made even more galling by the fact that the movie blows by a perfect, melancholy close about 20 minutes from its ultimate ending. Second, most of the effects are awful. Since at this point CGI technology remains unable to convincingly portray mass, giant open-ocean waves are not terrifying, but distractingly awkward. Third, the movie is lousy with cliches. From the rookie with a troubled past who rises to greatness to the grizzled veteran with problems of his own who gives the kid a hard time to force him to grow, we've seen all these characters before and we know them very, very well. Apart from the movie's Coast Guard setting, there's very little original to be found inside it. Got all that? Good. Because despite these obvious, sometimes major flaws, The Guardian is a winning, well-made film, the quality and pace of which come as a great relief in the sea of violent, cynical, explosion-laden nonsense that big studios generally sell.

The Guardian's troubled youngster is Jake Fischer, furiously played by Ashton Kutcher. As you might expect, the details of his past are not revealed until late in the film, but the questions are there from the outset: A highly recruited swimmer when he left high school, Fischer refused every prestigious scholarship offer and disappeared, only to surface at a Coast Guard training facility. Not lacking in confidence, Fischer nevertheless shrugs off questions about his past, preferring to focus on proving himself in this new world, and living up to the impossibly high standards set by Master Chief Ben Randall (Kevin Costner), the man tasked with turning the (vaguely diverse, appropriately motley) group of enlistees into elite rescue swimmers.

Cosnter's Ben Randall, meanwhile, is the movie's other comfortably familiar character. Reduced to a teaching role after a mid-rescue disaster stripped him of both his best friend and his confidence, and recently separated from his wife Helen (Sela Ward, who gives the Ben-Helen scenes a quiet gravity), he's depressed, frustrated and haunted. He also, as we've come to expect from such characters, has little interest in following the rules, and puts Fischer and his fellow trainees through a nontraditional training regiments so tough that both his subordinates and superiors question its utility on an almost daily basis.

So, there we have the set up: Troubled older man who's been through it all meets a golden boy with secrets. Needless to say, bonding ensues. And, perhaps surprisingly, this is where The Guardian really shines. Apart from a desperately misjudged sequence in which a swimming challenge is turned into a bad music video, the training section of the movie is immediately appealing, filled with winning characters (two-dimensional though most of the non-Fischer trainees are) and constructed with entirely convincing tension. The constant, confused back-and-forth between Fischer and Randall is confidently written and well-acted, and the ever-present subplots about Fischer's companions are well-paced and effectively handled. Simply put, director Andrew Davis (a former cinematographer who, in addition to several stinkers, also directed The Fugitive) and screenwriter Ron L. Brinkerhoff do things right. And, when graduation occurs, we're almost sorry, because we know it means we'll have to go back to the water; back to those horrible, fake waves.

And yes, we go back in the ocean (though, happily, much of the drama is played out in enclosed spaces, which limits the use of obvious CGI). There are arguments, rescues, several deaths and a completely over-the-top ending. But the movie, somehow, survives, largely on the strength of its two central performances. It feels odd to praise the inescapable Ashton Kutcher for his acting, but he's an undeniably magnetic presence here. Jake Fischer is a strange character of undetermined age -- sometimes he's portrayed as fresh out of high school, but more often he's an adult: Jaded and guarded, and almost paternal towards the trainees around him who need support. He's a bundle of emotions, too, leaping from blinding confidence to innocent confusion in the blink of an eye. And, in some ways, his erratic behavior can be reasonably traced to that murky, troubled past, and his resulting efforts to protect himself from getting too close. Kutcher, however, throws himself into every emotion with complete commitment, a decision that makes each change of mood and behavior entirely true, rather than constructed, or dishonest. The resulting character is weird and schizophrenic, but also totally irresistible. He possesses both an incredible, easy masculinity and an uncommon way of putting others at ease that are rarely seen in people so young -- and I'm talking here about both Fischer and Kutcher. Wildly erratic though it is, there's something thrilling about the eagerness of Kutcher's performance, as well as a suggestion there might be a lot more to him as an actor than he's previously let on.

Cast opposite the handsome, youthful Kutcher, Costner is perfect as Ben Randall. Settling into his age as an actor, he's clearly thrilled be playing someone, finally, who doesn't have to be sexy, or to get the girl. (There's a scene in which he climbs out of an ice-filled tub, unashamedly displaying scrawny, old-man legs that feels like a wonderful sort of confession, and a casting-off of all those old, looks-based roles.) Instead, his Randall is plagued by such bad back pain that he can hardly get up in the morning. He's alienated his wife and has no idea what he's doing with his life -- and the people around him don't even bother to hide their doubts about his competence. Weariness and self-doubt have always been in Costner, but here he gets to set them free: He's wisely low-key and subdued most of the time, convincingly portraying an unhappy, inward-looking man. What makes the performance a success, though, is the occasional unleashing of his familiar charms -- when he bonds with Fischer over beer and a bar fight, Randall's sudden impish, child-like glee is not jarring as it ought to be, but completely convincing because Costner wears it so well. In those fleeting moments, we get a glimpse of Bull Durham's Crash Davis, and Fischer sees, for an instant, who his instructor might have been just a few decades ago. The scene is effective on unexpected levels, and more moving that it probably ought to be. Like The Guardian itself, though, it works. Shut down the I'm-smarter-than-Hollywood part of your brain for a few hours, and just let yourself enjoy it.