I will come right out and say that I am much more of a Marvel fan than a DC one. Nevertheless, I feel Justice League deserves a chance, but it has to be delicately carried out. I'll give my opinions on what I would want for this film. I'm going against my loyalties, but it's not like it will ever match the MCU anyway. Now, with the knowledge that I've ticked off some DC fans, let's begin.
This movie has to be realistic with a slight dark touch. To put it simply, Nolan has to be at the helm. If this movie is even close to being as good as any of the Dark Knight movies, it'll be worth seeing. He should be the lead author. It has to be like Dark Knight, everything said is the perfect thing said and there are many memorable lines that can be imitated by fans with too much time on their hands. Like myself. The director should be Zach Snyder. He always makes the films visually appealing, and can do wonders with a good script. Get a bad script and you get Man of S---. I mean Steel. Which is why David S. Goyer should be nothing more than a plotter, or minor writer. I respect him for some films, not for MoS. I mean S. So, to recap; director-Snyder, writer-Nolan, little Goyer, producer-doesn't really matter, probably Nolan.
Now for the characters.
Superman: As you may have inferred, I did not like Man of S---. I mean Steel. It was long, boring, and poorly written. But I don't think that was Cavill's problem, so he deserves another go in JL. No point in getting someone else. The character Superman should be the de facto leader of the JL. He should be the glue that holds everyone together as a team, albeit loosely, and as an instrument for good. As there is no SHIELD to hold the team together, only the heroes themselves, a leader and some basic cohesion is needed. He should be moral, though I stress he must not be overtly religious! (33 years old, fights Kryptonians, one of whom said "You are fighting EVOLUTION, and if we've learned anything, it's that evolution always wins;" went to a church for guidance, etc. As an irreligious person I found that one of many disagreeable things about Man of S---. I mean Steel.) He should be inspiring, and the main public face of the JL as the most widely known member.
Batman: Christian Bale has come, and he has probably went. As a fantastic embodiment of the Caped Crusader, he CANNOT be followed up with a mediocre actor. Bale was good as both Batman and Bruce Wayne, and now that my gushing is over, the new actor doesn't neccesarily have to be as balanced. As Bruce Wayne himself will probably not be in the film due to secret identities and all that, the new actor should be more of a great Bat than a Bruce. In that case, off of the original choices for Batman Begins, someone like Cilian Murphy, who probably wouldn't be a convincing playboy but who could prowl the streets at knight in the cowl, is plausible, better than just some eye candy like Ryan Gosling, who I've heard about as a choice. In the movie, Batman should be like Tony Stark, a benefactor and a strong fighter. It might be hard to donate without revealing Wayne, but he is a secretive guy. He could even share benefactor duties with Green Arrow, coming later, or maybe the JL won't need funds or a headquarters yet. That would be a lot less strain, easier to write. In any case, he should have a power struggle with Superman, but eventually acknowledge that there is a job to do and to do it as a team.
Green Lantern: I did not see the Green Lantern movie. I was debating it, heard it was bad, then decided against it. Now, at least based on the actors I know, Ryan Reynolds seems like a good Hal Jordan as any, and he and Chris Pine probably would've been my top choices too. Nevertheless, I think that Hal Jordan should be in space somewhere, and John Stewart should take the role as chief GL for the JL. We can say he's Jordan's backup and just leave out Guy Gardner. This generation of moviegoers grew up on the JL cartoon with Stewart, and he's just as popular if not more so than Jordan. I'm not one to include diversity just for the sake of it, but here it is. I would cast Taye Diggs. The role on the team wouldn't be great, but he would probably be the big idea guy. He would side with Batman.
Flash: The Flash is one of the flattest characters in comic books. No compelling drive, no believeable origin story, next to no depth. With that in mind, Flash has to be the comic relief. I've also heard Ryan Gosling for this role, but it has to be a comedic actor. Neil Patrick Harris and Jay Baruchel are a few that come to mind. He would be a fast-talking, fast-moving (always, like even at leisure) wisecracker. He would be a fairly unaligned member, even towards the Superman/Batman polarization, but he would see things differently, and would end up being valuable in a key way.
Wonder Woman: Wonder Woman is lame. You can't deny. That's why the Lasso of truth, the invisible plane, and the star-spangled speedo whave to be completely absent. The one trait that remains; Amazon warrior princess. She has armor, sword and shield, and haughty, stilted demeanor. Whatever reason she is on the team is only enough to keep her from immediately leaving, and enough to have a minor concern in team chemistry, choosing Superman as leader. She doesn't have to be an uber-feminist, and shouldn't be, but the fact that she is the top warrior and royalty in a matriarchal society should have some impact on her character given the fact that she's on an otherwise all-male team. I don't have much of an opinion on casting(but the MCU got to Cobie Smulders first, people), but the actress should be tall, as Amazons are. However, thanks to movie magic, the actress doesn't have to be naturally tall. The same tech that made Chris Evans smaller in the beginning of Captain America can make her grow to Amazonian proportions. She should be maybe 6-8 feet on the screen, at least taller than the others, a towering figure.
Green Arrow: Green Arrow is a cool major member of the JL, certainly cooler than Aquaman, and he should be a founding member here. He has achieved popularity with Arrow, and is a rich guy, good with tech that could help the team. Now, the unwashed masses might mistake him for a Hawkeye rip-off, so I will commit a minor betrayal to my side and expose what I think Hawkeye didn't get into in the Avengers that Green Arrow could capitalize on. That is having an arrow for EVERY occaision. Bomb arrow, net arrow, homing arrow, double arrow, shock arrow, everything. As a head of a company, Oliver Queen could afford and/or build all that technology. He would be on Batman's side, as they are similar. Perhaps they know each other through business. I don't know. Now, I don't have the channel that Arrow is on or Netflix, but I've heard the actor is good, so he could do this, but the character should definitely have the blond goatee and the hood. Those are cool, recognizable character traits that establish a visual, aesthetically pleasing juxtaposition between a medieval Robin Hood look and modern technology. I can make a good sentence if I want to.
Aquaman: Aquaman is lame, and I personally would not include him. However, some people want him, so I'll say a few things. He would prefer Superman, which actually places him as a functional part, tying the vote between Superman and Batman, with Flash abstaining. Have you been keeping track of that? Huh? Moving on, I would use only the coolest powers, like raising waves and otherwise controlling water. As a prince, he would feel some empathy with Wonder Woman. I don't want to continue talking about him.
These would be the founding members, except perhaps sans-Aquaman. Then Martian Manhunter and/or Cyborg could come in in the sequel, and perhaps more people I may not know or care about in the third one. As for a headquarters, either Superman or Batman could provide one. I did notice that the base where Superman discovered Russell Crowe (I mean Jor-El) in Man of S---(I mean Steel) was in the Arctic, so that may or may not be a reference to the Fortress of Solititude, where the team could reside. Or Batman could provide a headquarters in Gotham, but that may seem a little too much like Avengers.
I don't know what event would bring all these different heroes together and keep them that way, but I'm sure Nolan can scribe one. It would have to involve Gotham and Star City (Green Arrow) somehow, be grandiose enough for Superman, far reaching enough for Wonder Woman (and perhaps Aquaman), and cosmic enough for Green Lantern. I would say that Flash would be brought in on Stewart's recommendation because Hal Jordan talked about him, referencing his friendship with Barry Allen and providing a basis for The Flash's comic apathy towards the team. It shouldn't have aliens to distinguish from Avengers, and given that the Masters of Evil might be in Avengers 2 or coming soon, there shouldn't be a league of more than two villains, or maybe three. I think Lex Luthor (probably introduced by that point in a Man of S--- (I mean Steel) sequel) and Sinestro would be good and easy to bring in everyone, although it might be weird if they are both Mark Strong, and then maybe a Wonder Woman or Aqua Man foe/usurper like Black Manta. I actually know him, that's one more than the Wonder Woman-specific villains I know. It can be scribed by Nolan, once again.
Well, that is it. If all those things were in there, I would definitely go see JL, though certainly not with more anticipation than Avengers: Age of Ultron. I wrote this yesterday with just Avengers 2, but I had to re-write it, and I can now include that name. It's not ALL bad. Anyway, as a Marvel fan I've been brutally honest with some of these characters (I'm talking about you, Aquaman!) due to my apathetic stance, but that might give me a advantage in determining the best possible way (without blind DC fanboy bias) for the Justice League to have mass appeal like the Avengers, yet be different enough from the Avengers to be a stand-alone great film. Please don't be too harsh with the comments if you're an Aquaman worshipper or something like that. I'm trying to help the DCCU. If that's a thing.