So, let me give you my spoiler-laden review.
I am not avoiding spoilers, so if you don't like them, stop reading here.
** You have been warned. **
The reviewers have not been kind. And I can see many of the same flaws they did. It's clear some things have been pared out of the film - just watch the trailers, many scenes are missing. Some reshoots needed to be done when the film changed the hands at the director's wheel.
Alright, so let's start with the biggest obvious chestnut of all: Superman is back. BTW, some rumors about the film (some spread by Cavill himself) did not play out. There was some suspicion he'd come back in a black suit with a beard, and be a bad guy, until they brought him back over to the light side. However: they do bring him back from the dead using a Mother Box, and for at least a brief while, he is kinda confused, and angry, and so - wearing nothing but pants - he proceeds to attack the Justice League, especially Batman, once he sees him, since they have a 'BvS' history. Fortunately, they have the ultimate weapon at their side - Lois Lane - and he snaps out of it once he sees her.
There were some rumors the League would have 7 members, not just the 5 featured in most posters, and they certainly have set up Green Lantern to join. "A" Green Lantern is seen in one of the flashbacks, but he's from thousands of years ago. However, in in the intro, an animated Green Lantern is featured. It seems almost certain they will have him in the next JL. But you don't see him in this film. I have my doubts it will be Ryan Reynolds, he's busy being Deadpool and his solo film bombed.
Flash provides a lot of comic relief for the film, his character is supposed to be young and awkward, new to the superhero game, a bit different from the way he's portrayed on his TV show, by a different actor.
The Aquaman in many ways seems like an angry, mean-jerk drunk; he's kind of the Wolverine of the team, he's a dick to everybody, though there's a funny moment of truth when he sits on WW's magic lasso by accident. Incidentally, he never uses aquatic telepathy, but he does say at one point he can talk to fish, but he says "it's the water that does the talking".
Wonder Woman seems to be emerging as the leader of the team, but she's afraid to step into that role.
Cyborg is an interesting character - in most of the comics world, he's usually part of the Teen Titans - but for a variety of reasons, esp. his connection to the Mother Boxes, they make him part of the League.
The Batman does most of the recruiting in the film, which is interesting, since as Comm. Gordon reminds him (played by JK Simmons!), apparently ever since Robin died (something they allude to very briefly in BvS), "he used to prefer to work alone". I gotta admit, of the movie Alfreds, I kind of like the Jeremy Irons portrayal. Michael Caine was a cool Alfred, but Irons' is a lot more "hands-on".
The film was supposed to set up the larger threat of Darkseid (who is Steppenwolf's superior) but it seems some of the edits were to make it more standalone. Darkseid and Thanos are very similar characters in the DCEU vs. MCU, as people have noted. The post-post credits scene seems to be suggesting Lex Luthor may be setting up the anti-JL of the Legion of Doom. Perhaps they will be the villains of #2, you also see Bruce Wayne beginning to buy and set up their own HQ of the Hall of Justice.
My guess is #2 (if they do a sequel; it's obviously been set up) will definitely feature Green Lantern, I mean he's in the intro to the movie. Then the question is who else will they add to the roster? First up are a lot of options from the DC TV shows -- like Hawkman/Hawkwoman, Firestorm, Atom, and Vixen, who have all been on Legends of Tomorrow; or also (Green) Arrow, & Martian Manhunter (who is on Supergirl).
Ironically, Atom on Legends is played by Brandon Routh, who WAS Superman in Superman Returns.
It's not clear where the DCEU will go from here. Unlike Marvel, they haven't been hitting it in the box office, and it looks like this movie won't do great. It's too bad, because a sequel where they build up the team and get their shit together cinematically might be good. I didn't think it was so bad - Suicide Squad was a lot worse. But then that may not be saying much.