With that in mind, what do you have?
Batman. Everyone knows who this is. The only difference to this Batman that I think needs introduction is that his main schtick this time around doesn't seem to be his batty obsession with his dead parents, but a sense of guilt over Superman's death. This is the first time that I've ever seen Batman depicted on film with friendship being a major part of his identity.
Wonder Woman. Everyone's favorite character at this point. The movie acknowledges some important parts from her origins movie earlier this year.
These two decide that they're going to start a team based off of cameos from previous films, consisting of the following three:
Aquaman: A bigger outsider than Batman ever was, and with a complicated backstory with Shakespearean family drama that's complicated enough that he's naturally the next one to get his own film. He reminds me a bit of the brooding Superman from Man of Steel, but it does fit the character a little better. However, he's the character who will probably endear people the least.
Cyborg: The most obscure of these characters, but at the same time can be summed up in one sentence. His father tried fusing him with alien technology to save his life, and now he's afraid of the technology that's taking over his body and possibly his mind.
The Flash: Barry Allen, everyone. Probably the most famous superhero outside of the Big Three. He says it as briefly as possible, that be got struck by lightning. Now he's fast, can go into some alternate dimension, and has the Speed Force. He doesn't have any friends, and it the most eager to join the Justice League. It should be noted that he is responsible for all of the movie's best moments.
They must fight Steppenwolf, a cool-looking villain played by a Shakespearean actor who delivers his few lines very well. He's of the Marvel variety, a forgettable villain; however, I personally really enjoyed him, if only because I really enjoyed the actor's performance. Steppenwolf's plan is to gather the Mother Boxes, an all-powerful force, and transform Earth into that red place that you saw in the trailers, which he would get away with if it wasn't for the Justice League.
That's it. That's the film in a nutshell. I think that it does a fairly decent job, and will keep people entertained. It doesn't have the gravitas and level of excitement and payoff that The Avengers did five years ago, but I think that people will be more satisfied if they go in thinking of it as a pilot episode for a DC animated show, since it has about a similar feel. There were certain moments that took me back to these kind of shows. Even Steppenwolf, as underdeveloped as he was, reminded me of villains who show up in a pilot episode to get introduced as a larger series villain who will get more development later.
I would also recommend this movie especially to people who haven't seen Man of Steel and Batman v Superman, on account of this film deciding to ignore major issues from them. It's very clear that DC wants to do a course-correct and wishes that they never made the first two films the way that they did, meaning that they're not only changing tone, but they're changing characters to fit their beloved comic-book counterparts with no in-universe reason.
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Other pros and cons:
Great cinematography. Everything directed by Zack Snyder looks gorgeous. In fact, I don't say this too often, but it looks even richer in 3D.
Poor sound editing. There were times when sound played an important part in storytelling, and it really should have been edited to make the film far more immersive.
The editing! This is where most people complain. It's very obvious that there are quite a few deleted scenes, because the scenes that remain, especially in the beginning, don't directly flow into each other and interrupt the momentum that the film is trying to build up. However, each scene on its own is pretty cool. The other editing problem is in Warner Bros.'s mandate to keep the film under two hours, including the credits. So the film feels like it's about an hour and a half long (hence why I compare it to their animated pilots), and that just wasn't long enough to build up some important conflicts and play off of character chemistry. I feel that the second act in particular could have had several extra scenes to help build up to several key character choices. The inevitable extended cut of this movie will probably drastically improve on this. However, it would have been nice to see all of these extra story on the big screen.
The music pleased me. Greatly. They distanced themselves from everything having to do with Hans Zimmer and embraced a lot of their more classical music that I hear from their television shows and their video games, and it took me to a nostalgic place. You hear hints of the original Batman theme, and the original Superman theme, and Wonder Woman's theme gets a makeover so that instead of playing on an electric cello, she makes her entrance to trumpets, which I think takes her good theme and makes it great. The best new piece of music easily belongs to the Flash. It plays whenever he goes into speed mode, and I truly loved it.
The costumes were great. The Flash once again gets my praise, because his costume is almost exactly what I always imagined that it would look like.
I will defend this film against comparisons to The Avengers, since most of the comparisons being made stem from similarities in the comics. Steppenwolf is compared to Loki on the basis of them both having horned helmets, but they both had those in the comics. The Parademons have been compared to the Chitauri, but the Parademons have been in the comics longer. The Mother Boxes as a generic source of power has been compared to the Tesseract, but again, this is ancient comics stuff. Most other comparisons after that come off as stretches, for me. Like, the fact that Wonder Woman knows who Steppenwolf is, and Thor knows who Loki is. Ahem, that's lame.
Anyway, I enjoyed it enough that for whatever reason I watched it twice on its own merits. I like these characters especially and it's pretty awesome to finally see them depicted on film. Especially the Flash. Goodness, can't you tell that I liked everything with the Flash?