The Gist: Upset by Superman's tremendous power and seeming lack of care for his actions, Batman sets out to neutralize him. Lex Luthor's son, however, might be the master puppeteer behind the epic confrontation.
Plenty of spoilers ahead.
Superman had finally been successfully rebooted with Man of Steel -- after an initial misfire (Superman Returns). Batman had just come off a very successful reboot trilogy, even though it now needed a new star and director. Why have them face each other now?
Apparently, DC Comics and Warner Brothers (which owns the DC catalog), were either concerned or jealous of Marvel's continued success at the box office in developing franchises for both individual superheroes and collectives (with The Avengers), so they wanted their own.
The problem I see is that they simply weren't ready. They jumped the gun. They wanted to have a blockbuster that set up a franchise that involved several superheroes, but only one was established in its current form, Superman. The new Batman, brought to life by Ben Affleck, was completely untested. No other character was developed at all.
Furthermore, the villain doesn't fully work. Lex Luthor is played here by Jesse Eisenberg. Eisenberg is a very good actor, who shone in The Social Network, but here he's virtually playing a crazier version of a jacked up Mark Zuckerberg, and he recalls too much Kevin Spacey's performance without nailing its subtleties. Maybe he was going for something like Heath Ledger's Joker, but if that's the case he failed.
But wait, there's more! The producers were probably under orders to establish individual superheroes for future standalone movies, so the Flash makes an appearance (as do Cyborg and Silas). And then of course there is Wonder Woman, played by Gal Gadot.
Her character is actually one of the coolest things in Dawn of Justice, besides the eye popping visual effects of course. Gadot seems perfectly suited to play the Amazon in next year's standalone Wonder Woman, so I'm actually quite curious to watch it.
And then there's the last nail in the coffin of this uneven effort: the creature Luthor concocts from General Zod's corpse. I'm sorry, but swallowing that is really asking too much of the audience.
So many questions... Why would the spaceship still sit in the middle of Metropolis? How could a politician think it perfectly okay to hand over very powerful alien technology to a private individual who has immense wealth at his disposal? How did he quickly figure out a way to reactivate the ship and use it to create that monster while no other scientist had? How is it supposed to look like an even fight when the creature is clearly more powerful than even Superman, given they have the same physiology and therefore the same superpowers, and it's enhanced?
Ultimately, when the movie ended I just felt sad and sorry. Sad for Affleck and sorry for the 2 franchises. Warner Bros. had a good thing going with Superman, but they should have given the perfectly cast Henry Cavill the chance to build his bonafides a bit more.
I felt sad for Affleck because he was done a disservice here by not being allowed to build his own character at all before being thrown into a tussle with a superhero he sees as a threat based on the most risible of assumptions. Batman is supposed to be incredibly smart, first because otherwise he wouldn't have the empire he has, second because he wouldn't be able to keep his identity secret so well, third because he's always outsmarting all the bad guys. But if he's so smart, then how does he not understand that Superman had no choice but to fight against General Zod with all his might? Certainly there was a lot of destruction and some innocent people were hurt or killed in the exchange, but if he had not fought back against Zod, the latter would have wiped out humanity completely and terraformed Earth to his likings!! Would that have been better?!?
Frankly, the whole premise the film is based on, that Batman has some beef with Superman, which leads to a confrontation, is ridiculous. And that undermines the whole structure of the plot.
The Bottom Line: Batman v Superman: Dawn of Justice is not a horrible movie, nor the worst superhero movie ever made. It's just too implausible, even for this genre, it's based on too flimsy a premise, and it tries too hard to be something it doesn't have to tools to be.