The editing is atrocious. The first half hour of the film plays like a series of tongue-in-cheek trailers introducing each character. The actual scenes are fine; Deadshot and Harley's introductions are on-point. But it's framed with Amanda Waller having an extremely awkward expository conversation with a government bigwig over dinner (who is conspicuously not the same government bigwig from the first trailer), and the whole thing feels clumsy.
When it got to introducing Enchantress, I literally winced. Even Thor handled the supernatural elements better than "she's a witch, deal with it." (Thor implied that the Asgardians had just hit Clarke's Third Law; Suicide Squad straight-up says she's a witch, no explanation given.) Not to mention that her host, June Moone, gets incredibly little characterisation; given that a lot of the narrative relies on us giving a shit about her, this is a mistake. I did like Enchantress' design and the aesthetics of her introduction. It was very creepy and weird, and if the dialogue around the character wasn't so bad, I'd like her. But for some reason, from the second act onwards her appearance shifts from "creepy prehistoric witch" to "Cara Delevingne in a trippy dress," and it ruins whatever gravity her character had. She switches back to witch-mode at the end, which I appreciated.
It improves significantly in the second act; everything after the Suicide Squad actually assembles is pretty good. Then it peters out a little near the end, but still kept my interest - there's a wonderful scene which is just the Suicide Squad saying "screw this" and breaking into a bar to have a drink instead of saving the world - and then the climax is full of cringe-inducing "I love you guys so much!" dialogue that feels like a "the TRUE power was FRIENDSHIP" message. Which...does not gel with the rest of the film, at all.
It is a pretty funny film. There's a good balance of comedy and action; it actually pulls off the comedy much better than the drama. Most of it comes from Harley and Deadshot, but there's a few gems from Killer Croc as well (if you can make out what he's saying.) It's also quite colourful; it takes place mostly in an urban area at night, but makes heavy use of bright neon colours to contrast the gloom-and-doom.
The main antagonists through the film are these very creepy-looking eyeball monsters that reminded me of Bloodborne [http://vignette2.wikia.nocookie.net/bloodborne/images/7/7c/Bloodborne%E2%84%A2_20150512194836_-_1.png/revision/latest?cb=20151013162329] a little, which was neat. There's a very eldritch-horror aspect to the villain that unfortunately gets undercut by their very generic motives.
Overall, the writing swings between "Pretty funny!" to "Jesus, I can't believe someone wrote that and then asked Will Smith to say it." There's no major plot holes aside from two very big ones: the "why don't you just drop a missile on them" solution, and a scene where the Enchantress proves her chops to an unnamed general by teleporting to Tehran and stealing some classified Iranian military documents...which are in English. Perhaps she also translated them for the general's convenience?
The entire plot is essentially Amanda Waller trying to clean up her own mess, which is both kinda funny and appropriate. If I had to pick a low point, I'd say it's the shoddy and inconsistent editing; it's most noticeable at the start, but it's a problem throughout the whole. The first third of the film makes a very poor impression as a result.
If I had to pick a high point, I'd say it's the acting. Everyone is on-character, the costuming is great; Will Smith, I hate to say this, is actually pretty good at Deadshot, Margot Robbie does a remarkable Harley Quinn, and the Joker is, despite his weird-ass punk kid costume, actually very close to the source material as a psychopathic gangster as opposed to Ledger's anarchic terrorist-philosopher. Though - and all respect to Jared Leto, I know he went literally crazy for the role - I still prefer Ledger. Leto's portrayal just grates on me.
It's a solid 5/10, and I say that honestly, not on a four-point scale. It's not bad, it's not great, I had fun watching it, I wouldn't go watch it again, and if you're a fan of the title or of Harley Quinn as a character it's worth seeing. If you were looking for the fabled DC franchise-saving magnum opus, this isn't it.
It's getting shat on by Rotten Tomatoes, because of course it is, but honestly, it's about as good as Assault on Arkham, and people really liked that adaptation, so whatever.