Two stars because it should have just been included in the game. ALL DLC gets low scores.

Beyond that:

The good: Batman. 'nuff said.

The bad: It's DLC.

The ugly: The box art

Harley Quinn's revenge is, in essence, too short, not very fulfilling, and the difficulty curve is all over the place. At one point, you have a very ho-hum fight with three thugs, almost immediately followed by an absolute deathtrap involving a large group of fairly varied thugs. The padding is usually quite obvious, as in the case of "hunt three thugs to get the 7 letter passcode for a door", and the writing does Harley no favours, essentially only emphasising how stupid the writers seem to think she is.

Even with the padding, this was finished in under an hour, as there's little to no incentive to explore or interact beyond the strict bounds of the area, and, for the price, it just wasn't worth it.