I had a feeling that if they were going to make a movie where "Harley Quinn" is about half of the title, she would steal the show. And I was right! Unfortunately, the show which Harley stole was not not a very good one...
At first I didn't know how to feel about this movie. I grew up on the "Batman the Animated Series" cartoons which this movie spawned from. Those cartoons always took themselves very seriously, and explored themes that were pretty dark and complex for kids shows at the time. However, that show ran in the '90s, and it's 2017 now, and Batman has been pretty thoroughly explored and picked apart on TV and in film since then (see The Lego Batman Movie).
Maybe because of this, I think Paul Dini and Bruce Timm decided they would try a different route than what one might expect from the original cartoons: this movie DOES NOT take itself very seriously. Harley Quinn is good for that, she is making jokes and acting silly throughout. Batman and the main villains take themselves very seriously, but literally no other character in the movie does. About half of the jokes and antics are funny, and the other half fall pretty flat. Comedy was never the original series's strength though, in fact jokes falling flat was the norm. That normally wasn't a problem in the original series though, because the story, mystery, or character development was the focus, not the humor.
In this movie though, the story is pretty generic, there is no mystery, and there aren't very many new or interesting characters to develop. On top of that, the focus of this movie is shifted more onto the humor and to Harley Quinn's various antics, which makes it feel, well... really CAMPY. Honestly though, many of Batman's iterations over the years have been quite campy (RIP Adam West) so I would bet there would be many fans of Batman who would not see this as a problem.
Where it does become a bit of a problem is when some characters act VERY out of character with minimal explanation as to why. Without spoiling anything, one scene in particular has a character act EXTREMELY out of character for what I have to assume is only for the sake of "fan service" (if you see the movie you'll know what scene I'm talking about). Combine this fan service with the campiness and you come away from this film feeling as if you just saw someone's fan fiction brought to life. Admittedly it's not really BAD fan fiction, but it is very AVERAGE fan fiction.
Truthfully, even with all of that I could easily justify giving this movie a 710, or maybe even an 810 if you really enjoy camp. However, THAT ENDING THOUGH!!?!?! Without spoiling anything, the movie's ending is abrupt, overly silly, and anti- climactic. They really build up a character appearance and an epic fight, but the payoff is instead that the character leaves as soon as they arrive, a silly moment happens, and then the film pulls with a Looney Tunes-esque moment. It felt like suddenly Harley Quinn became the director and directed this final scene. It felt like I was trolled by Paul Dini and Bruce Timm. They might as well have played the movie out to the tune of Rick Astley's "Never Gonna Give You Up". I knocked two whole points off of my rating just for that ending!
It should also be noted that there are two stingers in the credits: one that happens a few minutes into the credits, and another that happens after they have ended. Both are pretty silly. In addition, after the final stinger, there is a short interviewbehind the scenes look in which Bruce and Paul and others are asked about the origins of Harley Quinn, a look at what her real-life sociopathic disorder would be, and just a description of her as a character. It's good, as good as or possibly even better than the movie that came before it... In fact, I added a point back onto my score because it was good. Admittedly it did feel a bit like they were justifying some of the poor decisions being made in this movie (including the fan service one...) but still cool to know!
So overall, it's a very okay movie with some problems, but was still fun to see.
Review by aserpentperplexed from the Internet Movie Database.