Most people tend to think of Harley Quinn’s relationship with the Joker as her primary claim to fame. But the new solo Harley movie delivers an enjoyably quirky and unapologetically feminine piece that starts off 2020 on the right foot.

Superheroes are kind of a big thing right now. They’ve already conquered the movie market and started making progress on video games, and recently, the capes have decided to come back to the small screen. While...