I'm a sucker for tales of teenage girls, so this combination of coming-of-age story and possibly fatal disease worked for me, even though the latter isn't my favorite genre.
The team behind Babyteeth have worked under the radar. This is director Shannon Murphy's first feature, and I didn't know her, but she's been directing series television since 2013, so she's no amateur. This was also the first writing credit for Rita Kalnejais, although again, she's no amateur ... Babyteeth is based on her stage play. Not sure it means anything, but as of this writing, Kalnejais doesn't even have a Wikipedia page, which can also be said for Toby Wallace, who plays "the boyfriend", and Eugene Gilfedder, playing a music teacher. And once more, these aren't amateurs ... Gilfedder has acting credits, mostly in TV, going back to 1993, and young Wallace also has plenty of TV credits. So, unknown to me, sure, but they weren't hired to give the "authentic" feel an amateur offers.
The female leads, though, are people I know, although in both cases, they snuck up on me. Eliza Scanlen was Milla, the teenager with the terminal illness; she looked familiar, and at first, I thought it was because she kind of resembles Alison Pill. But actually, she's been in a couple of recent things, the HBO mini-series Sharp Objects, and Greta Gerwig's Little Women (she was Beth). As for Essie Davis, who played Milla's mom, all I knew about her was that she was in The Babadook that I love so much, and I commented early on that I didn't remember her in that movie, that in fact, all I could remember from The Babadook was the mother and the son. Imagine my embarrassment when I finally realized Davis was the mom in Babadook! (Hey, her hair was a different color.)
Just about everything works in Babyteeth. Scanlen impressively goes through a lot of different emotions. Toby Wallace is believable as the "dangerous" boyfriend (someone mentioned that they were reminded of Valley Girl). Davis has a stereotypical role (middle-aged mom with a drug problem) ... actually, much of what happens in Babyteeth reminds us of standard weepies, but it feels fresh just the same ... anyway, like Wallace, Davis is believable as a character you don't usually see outside of movies (and she gets the movie's best line: "This is the worst possible parenting I can imagine"). Toss in Ben Mendelsohn as the dad, and you've got a very capable cast. Murphy is unafraid to step slightly outside the lines in her direction, and whatever Kalnejais did in the transfer from stage to screen is seamless ... not once did I think, "this is based on a play". As many critics have noted, Babyteeth is familiar enough to trick us into thinking we know what is coming, and quirky enough to frustrate our expectations just the same.
And it's funnier than the above might suggest.