An inevitable problem with seeing a movie weeks after it opened, and then only because of the many good reviews I've read, is having nothing original to say about it. This I already knew.

Such is my experience with Half Nelson, the Sundance-beloved drama about an inner city history teacher with a crack addiction and the 13-year-old girl whom he doesn't quite befriend, exactly.

Frankly, part of the problem is that having that sentence laid out, nothing about the film needs to be said anyway. A teacher film is always going to be a teacher film, and no-one can doubt where it's going: the troubled girl and the troubled teacher will learn from each other and strive to better themselves. And since it's an indie, they won't succeed in the film itself, although it ends hopefully.

And also since it's an indie, set in the inner city, it's going to have a very specific look to it: handheld everything, shot on 16mm film for that extra-gritty verité gravitas, even when you'd really be a lot happier if it wasn't (in particular, the final shot suffers mightily for being handheld - I was thinking more about the fact that the frame was moving up and down than about the content of the shot). Lots of long takes. Sounds like it was shot in a tin can, and the music is all recorded on set. Once upon a time this grittiness and lo-fi sloppiness was bracing and the sign of DIY passion; now it's become a stale cliché that signifies "realism," with those exact scare quotes. What would be truly independent is if a Sundance kid shot something with bold expressionist colors and angles, a touch of gloss. Director Ryan Fleck is no hack, but he's not very edgy, either.

That said, despite how totally unshocking and unoriginal the story, themes and appearance of Half Nelson (and while I'm ragging on the film: that title doesn't make half a damn of sense), how completely correctly I guessed every inch of plot and every cut, I loved it. The reason I loved it is because of two wildly gifted actors, Ryan Gosling and Shareeka Epps.

Gosling plays Dan Dunne, the dialectic-espousing teacher. At the time of shooting, he was a mere 24 years old, and I cannot name another performance by an actor under 25 in the recent past of such commitment and passion. There is not a trace of "acting" in the character. The script, to its credit, does not give much away explicitly, and this simultaneously allows and forces Gosling to embody unspoken ideas: we are fully aware that he is disappointed in himself, perhaps trying to passively commit suicide, and that only his devotion to his job and "his" kids keeps him sane and part of the world, and we are aware of this not because the script tells us anything, but simply by the way Gosling stands, walks, mumbles. In a more perfect world, this would be a star-making turn; in our world, we must settle for the tiny clutch of people who make up the audience for this kind of film being treated to a truly spectacular performance.

Shareeka Epps holds her own - it's unimaginable she could do more - as Drey, a girl who finds Dan high on crack, and begins a strange sort of pas de deux with the teacher. On paper, it makes no sense at all: Drey is strong enough and smart enough to know that Dan will never amount to anything, and will only ever be a liability to her. But Epps creates a sort of empathetic kinship that the script doesn't quite provide, and it makes her character's arc infinitely more understandable. Dan is, in some strange funhouse way, the future version of Drey's current life, and by studying and saving him, she's ultimately investing in her own fate, and this parallel simply could not be possible with Epps' performance, which both mimics and runs against Gosling's in ways that make perfectly clear what Drey feels throughout the story.

Between these two actors, Half Nelson turns from predictable to beautiful and humane: as written, nothing about the characters is particularly affecting or interesting, but because of the performances, Dan and Drey turn into the people that co-writers Fleck and Anna Boden wanted them to be: individuals who realise in a quiet and subtle way that their lives aren't right, and that their world isn't going to allow them to change, so they must change it.

A last thought: the one unabashed achievement of the script is its racial politics: Dan is white, his class is almost exclusively black, and late in the film he decides to save Drey from the black drug pusher who pals around with her. And excepting only a dinner between Dan and his family, this is not commented on: Dan's race could change and the script could stand almost entirely without change. That the film should be so fundamentally and unexplicitly about race is truly brave in American filmmaking (it is the complete antithesis of Crash) makes it far more effective than any film which stands up and crows about black and white people getting along could ever be. Class and race are not absent, but you have to look for them, and that means you really have to think about them, and that is almost enough to recommend the film all by itself.