We're first introduced to our rogue's gallery of supervillains ("metahumans" in DC's terminology) with flashy graphics and video clips of them in action, both out of prison and in (where they are now). And we're introduced to Amanda Waller (Viola Davis) and her plan to use these people to defend the planet against future metahuman threats. Not surprisingly, her control over one of them is inadequate, and by letting them out she creates her own first problem to solve. Nobody ever bothers to point this out, and there are essentially no consequences for Waller. I realize that superhero movies are getting darker and "consequences" are a thing of the black-and-white morality of older comics, but she made an epic mess and no one even mentions it?
Our crew is Deadshot (Will Smith being Will Smith), Harley Quinn (Margot Robbie - selling sex appeal with a side of crazy), El Diablo (Jay Hernandez), Captain Boomerang (Jai Courtney - haven't much liked him before, but he's very convincingly unpleasant here), Killer Croc (Adewale Akinnuoye-Agbaje - all prostheses and fangs), Sorceress (Cara Delevingne acting badly in a skimpy outfit, covered in dirt), and Slipknot (Adam Beach), with Rick Flag (Joel Kinnaman) and Katana (Karen Fukuhara - a placeholder if ever there was one) riding herd. Oh, and let's not forget The Joker (Jared Leto - so method he stayed in character for the entire filming schedule), who's been missing Harley since she's been locked up and is determined to rescue her. With such a large cast in a comic book movie, it'll come as no surprise that character development takes a back seat to action set pieces - and as weak as the character development was in the Marvel ensemble movies, at least those characters had been developed in previous movies. These characters are both new and under-developed.
The movie is ... okay. Which is a higher rating than I give to Marvel's ensemble "Captain America: Civil War". I liked some of the characters, although none of them got enough air time. Except Deadshot, who got more screen time than any of the others but was just ... Will Smith doing his usual thing. I mean, Smith is a good actor, but he does absolutely nothing new here.
DC is also borrowing a page from Marvel's playbook, using a mid-credits scene to set up upcoming movies - in this case Batman's interest in other metahumans for "Justice League."