Just got back from it. I won't spoil anything, and I'd advise whoever doesn't want to get spoiled to stay off any websites related to the movie, as I'm sure someone will drop the bombs soon.
Whoever was clamoring for more uplifting aspects of the Superman myth to pop up on the screen - this is not that kind of movie. In fact, it's a lot darker than Man of Steel. Even the more savings and more uplifting aspects of the character are presented in a very dramatic, melancholic and gloomy way. The movie deals with the repercussions of what happened in the previous movie, and they're not very nice.
Other problems of the movie are its tonal inconsistency and the fact that Zack Snyder lacks any subtlety (if you thought Christopher Nolan wasn't subtle, wait until you hear the infinite dialogue about God, Gods, power, heroism, Greek myths, God, The Devil, Gods, etc.). He tries to present deep themes, but hammers them into the narrative. Explicitly. Again and again. And again. And then there are aspects of the action and Zack Snyder's style which are plain ridiculous (I'm talking about the final fight), which maybe would work better if the movie wouldn't take itself so seriously. But it'd still be CGI overkill. And Wonder Woman...
She's kinda cool. Kinda. Because she's also very useless and her only reason to pop up in here is to set up the future Justice League. She doesn't bring anything else to the table... well, if we count out that she shows off her moves amidst the CGI-heavy climax.
On the other side, though... Henry Cavill and Ben Affleck put their heart and souls into their roles. The new Batman is kick-ass. There are some genius moments in the movie, and the themes presented - ARE INTERESTING. The story touches several very interesting points. Not in a subtle way, and initially not in a way that actually brings anywhere. I was starting to worry this would end being another Zack Snyder Watchmen, where profound conceps are merely thrown on the screen, without any sincerity or knack for character for or real human emotion. But there's one very redeeming scene, which ties the (intially empty) drama of the story together, and made me look at the entire first half of the movie in a different light...
...and then we're back in 'ridiculous territory.' And then it gets interesting again. And another kick-ass scene. And then another cringe-worthy one.
- and this is Batman V Superman in a nutshell: it's an ambitious and bold take on superheroes. But it's also pretty inconsistent and messy.
If I had to give it a rating, it'd be between a B- or C+. I have yet to decide. I'll need some more time to ponder and take it in.
I'm sure looking forward to the future DC Universe, though - so much I can tell you. It's going to be a very interesting ride.