Just thought I'd delve a little bit further on the nuts and bolts of it.
It's a good, fun, summer/superhero movie. It has some massively weird structural problems, especially during its first third; the opening scenes a basically just stitched together in a manner so artless it becomes baffling. The only thing signalling one scene ends and the other begins is the waaaay-too-cute change in needle drops, which becomes comically bad before the film's 5-minute mark. Seriously, when the opening to "You Don't Own Me" starts - out of a jarring 2-second silence- and we see Harley Quinn's legs, I thought I was in a 90's JRPG in which a character's theme song starts playing simply because he/she shows up.
Another thing that is utterly bizarre is how repetitive the film is in its beginning. It's a sin the film commits again later on - in an explanatory rehash of previously played scenes that might as well have had a subtitle with the words "WE ARE SHOWING THIS TO YOU AGAIN BECAUSE WE THINK YOU'RE TOO DUMB TO FIGURE OUT THIS SIMPLE PLOT BY YOURSELVES!" - but it's just bizarre in the start. We literally see and hear how great Deadshot is with guns at least 4 times within 20 minutes of film.
Now that the main negatives are out of the way, allow me to say that the film gradually comes into its own quite nicely. As the story progresses and possibilities for digressions diminish (not for lack of trying, though; the film throws curve balls to shoehorn the Joker in for no dramatic or narrative reasons whatsoever), we get to see these characters and actors interact with each other and, in those moments, the movie sings.
Even the lesser characters are played in an entertaining enough fashion that they become interesting. Katana, Captain Boomerang, Killer Croc and even Amanda Waller (a leading role) have basically no character arc throughout the story, yet they are played by actors who have enough charisma and/or flair (yes, even Jai Courtney, who is a slimy delight in this) that you want to see more of them.
It's almost as if this film is hampered by its plot getting in the way of its wonderful characters. If I had to pick, I'd say Jay Hernandez walks away as the MVP. His character is a walking embodiment of the film's themes, a basic model of what the other main characters end up aspiring to be. In a weaker actor's hands, the role would be the most cloying, obvious thing ever. Hernandez gives the guy an equal measure of heroism and self-loathing to make him a beautifully endearing person.
The 3 leads are, unquestionably, Smith, Robbie and Kinnaman (surprisingly good here). Smith is an expert at balancing movie-star quality and character work, and this is a testament to his talent. It's very much a Will Smith Starring Role (tm), yet you still get a sense of who Floyd Lawton is as his own person.
Robbie is an explosion of charisma and sex appeal come to life. Her accent (and, to a lesser degree, her performance itself) oscillate all over the place. She goes from a damaged woman to a Saturday Morning cartoon character within seconds. Yet, somehow, it works almost all the time (I'm a stickler for accents, so that's also an issue). Some of her zaniness is a little too forced, but she manages to make Harley both a cypher and a force to be reckoned with well enough to be fascinating throughout.
Kinnaman plays what could have been a very bland romantic lead very well. Like Robbie, he flies all over the spectrum, especially in the film's first half. After a while, though, he portrays his character's gradual bond with the team with wonderful humanity.
Sadly, I can't say the same for his romantic pair. Cara Delevigne looks fantastic on camera and, while she sells the frightened human side of her role, her turn as the villain of the film is mostly dull and sometimes even embarrassing. When she goes full evil witch, her performance would have been more in place in a Ghostbusters film than this. She plays Enchantress as a cartoon character in a children's film.
I have more to say , but I thought the movie worked very well, even though this post was mostly filled with complaints.