I thought it was great. Most of the criticisms are pretty unwarranted in my eyes.
Sure, the first hour is a bit slow, but it's all setting up completely necessary story material; it's not like it drags its feet for no reason. Everything adds up to something, or is obvious setup for the future. I have no problem with that.
People also complain about seeing Batman's parents being murdered once again, but I'd honestly argue that even though I already know the story, this is easily the single most beautifully-shot and emotionally-effective rendition of that origin I've ever seen. Makes Nolan's version seem ridiculously weak and un-cinematic by comparison.
People also complain that the two characters fighting makes no sense, because these are supposedly two of the smartest men on the planet, and one would think they could have just talked it out. The people that complain about that apparently missed Affleck's line (that was even in the trailers) about how "if we believe there's even a 1% chance that [Superman] is our enemy, we have to take it as an absolute certainty." Kind of spells out his single-mindedness on the subject right there. Not hard to grasp. Superman could bake Batman cookies, and it wouldn't change the fact that he could potentially be a walking (slash flying) WMD.
Likewise, the complaints about the "Martha" scene are absolutely silly. Honestly, why can't anyone wrap their heads around why Batman turns himself around in that moment? It all felt pretty reasonable to me. People play dumb and pretend that it's just that their mothers have the same name; obviously that's the dumbest conclusion one could come to. Batman's attitude turns around because, in potentially his last moments alive, Superman cares more about his human mother's life than he does about his own. This marks him not only as being heroic and good, but also as being just as human as Batman himself. He's not the potentially evil alien Batman assumed he might be. Meanwhile, the fact that her name is Martha offers Batman some tiny chance at redemption for the actions he obviously couldn't take as a child. A mother named Martha is on the razor's edge of being murdered, just as his own mother once was, and he has the chance to change it this time. For an emotionally-damaged character like Batman, the benefits of a moment like that ought to be obvious.
I find it funny that while everyone complains about Nolan's movies for overexplaining everything, people also complain when they're offered something simple to interpret for themselves, but can't seem to wrap their heads around it. Silliness.
I can, however, understand the complaint that Luthor's involvement doesn't seem to make much sense; it's never clearly explained why he's doing what he's doing. But there are hints, which I understand if people missed.
He talks about equating his powerful father (who was abusive) to being somewhat god-like, but also explains the idea that a god can't be all-powerful while also remaining all-good, just as one can't be all-good and be all-powerful. Basically, his dad was all-powerful but a total asshole. He has daddy issues.
In a weird way, I can almost look at the story as being like a Superman equivalent to The Killing Joke. While Joker's plan in that was to prove that one bad day can drive even the sanest of men mad, in BvS it seems like Luthor is trying to prove that Superman (the "god" in question) can't be all-powerful and all-good at the same time, by forcing him to kill again.
That is, of course, not even mentioning the deleted scene they released online, which shows that Luthor was obviously under the control, to some extent, of outside forces (the New Gods of Apocalypse, or maybe Darkseid himself). That's their bad for not putting it in the theatrical release. But it should be in the bluray cut, so it'll be interesting to see what else was missing.
Meanwhile, that also leads to the most interesting thing about the entire movie, in my eyes; the idea that the Justice League will need to protect Lois (Superman's anchor to humanity) in the future to keep Superman from going bad, as he did in the vision of the future that Batman has.
Sure, there's the idea that the League needs to exist to protect humanity from encroaching evil, blah blah blah... same reason the Avengers get together. But there's also the fact that they need to be there to keep Superman, the most powerful, potentially dangerous being on the planet, connected to his humanity. They have to be babysitters.
It's an interesting angle, and I'm really surprised that Warner Bros. is approaching so much of this stuff from slightly more subtle, less-obvious angles. This shit really was made for the fans who dig the less-mainstream ideas. For all the talk of how the move is just a big dumb slugfest, there are a lot of deeper ideas in here that many don't even seem to have picked up on.
Also, am I the one one who picked up on the way the movie is dark and bland and grim in the beginning, but once the Trinity finally shows up together... suddenly it's colorful as hell and feels way more like a classic DC Universe sorta thing?
I felt like that was a signal, that the future movies in DC's film universe are going to be a bit more comicbook-proper, in a way. Suddenly you've got much more in the way of costumed heroes stomping around the world, and everything is going to be brighter and more "fun." For all the talk of how dark and mean the movie is, I actually thought it had a really hopeful ending to it, which, in my eyes, seems to point toward future movies which might be more in-line with what people want out of these characters. They just had to properly build up to it.