I'm not sure exactly what happened in the editing but it certainly feels like they made adjustments to the soundtrack because of the popularity of Guardians of the Galaxy's soundtrack both as an album and toward adding a nostalgia factor to the movie. Suicide Squad really overdoes it and plays like an impatient listener hitting skip on a mix CD every 30 seconds as the scenes changed.
The movie doesn't know how to start. It gives a couple of title cards then jumps right into two scenes that aren't especially establishing for the movie as a whole. They are just scenes of Will Smith and Margot Robbie in prison that just seem to be establishing that they are in the movie. It's a start that just falls flat. The first act of the movie pretty much takes place in a dinner meeting with a dossier (they're all a little too cavalier with their dossiers, leaving them around, and filling them with absolutely every fact they have about people and things so that characters can learn everything there is to know about any subject). This meeting runs through a series of scenes like they're checking off a list of skills, how they were caught, and chances for hero cameos.
The villain of this movie is inserted in a pretty sloppy way, and the flashback that shows one more fact to make sense of it, doesn't add enough to feel like it's worth while (it feels like they just repeated the scene later). Cara Delevingne is an odd actress for her part. She does give it her all when physically becoming the Enchantress but that turns into seeming as though they just told her that her character can never stop moving. I think for this movie, the stakes of the villain were a little too big, and the personal stakes of every character were very heavy handed and overdone.
Will Smith, Jared Lato and Margot Robbie all do very good jobs of playing their parts. Each one of them seemed to bring a full character that was unique and easy to watch. Will Smith has a character trait of strutting as he walks that gradually rubs off onto every other member of the Suicide Squad. It's interesting this was used to show the growing unity of team, but they also ended up looking like a group of middle school boys trying to look cool.
This isn't the worst movie ever, and it really felt like the edit was one of the biggest problems. It's not as bad of a movie as the reviews but it's not a movie that should have had more positive than negative reviews. In a way, the successful marketing that built up the hype for the movie was what ended up hurting it, not just because of the changes that were made, but because critics came in expecting one thing and got another.
Successful marketing really is all that matters because it got ticket holders into theaters and resulted in enormous sales in the opening weekend for Suicide Squad. Odds are, it made enough to get another try for DC comics, and a Suicide Squad sequel.