I actually thought the start was the best thing about the film. It was stylized and unique and gave the characters it chose to focus on due attention and, well character. As soon as they get on the helicopter, or rather as soon as the villain is revealed, I felt like the movie took a swan dive into mediocrity and had to swim through waters more toxic and polluted than Rio to get to the end.
So much of the movie is painfully generic, especially since one of the biggest plot points was done by DC in Man of Steel 3 only 3 years ago and made even less sense in Suicide Squad. The movie has some good performances, and 3 really good characters IMO, but most of the cast is only there for posters and montages and so much of the story either makes no sense or circles back on itself unnecessarily just to continue on.
I almost want to know what was cut out to see if it would make the film any better, kind of like BvS. Goodness knows, Leto would love to have some of his stuff put back in (as well as all the scenes which were in the trailers but nowhere in the movie, great marketing there) though personally I’d have preferred it had they cut him out entirely. Waste of a Joker, which is not something that I should be able to say.