"I had sex today. Holy shit." And so begins The Diary of a Teenage Girl, a well-acted, well-written drama that does everything it set out to do, though the movie didn’t hook me like it has some others, including my fiancé.

We soon learn that the man this plain, self-described "ugly" 15-year-old had sex with is her mom’s much-older boyfriend, and that’s only the beginning of her sexual exploration in 1970’s San Francisco.

Bel Powley plays the protagonist Minnie, delivering an understated, mindful performance as a girl whose sexuality is blossoming, even if her curiosity is misplaced at times. Powley embodies the role and is impressively convincing. As the boyfriend, Alexander Skarsgård delivers a fine performance as well, though his character is underdeveloped and not nearly as three-dimensional as it needed to be given the role he plays.

Nonetheless, The Diary of a Teenage Girl, written and directed by first timer Marielle Heller (working from a novel by Phoebe Gloeckner), is a rich piece of filmmaking, an immersion into the teenage mind. There’s real substance here and the script is fluid and engaging.

On the flip side, the movie never hit me over the head the way I was expecting. Heller places a lot of emphasis on the less-than-proper relationship between Minnie and her mom’s boyfriend, but in that regard, I expected more from the obvious conflict that arises. And if The Diary of a Teenage Girl is not supposed to be about that specific relationship, and instead about Minnie’s sexual exploration, Heller fails to place significant weight on the other story arcs.

The Diary of a Teenage Girl is a well-made movie that features a strong performance by Bel Powley, but it leaves some potential on the table. As a debut directorial effort, though, Diary is a worthwhile entry.

Review by Erik Samdahl.