So it took me a good long while, but I finally got around to seeing BvS. And to be honest, I thought I was going to hate it, but I actually ended up thinking it was OK. Not great, but just OK. I think it helped that between the disappointment that was Man of Steel, the dreariness of the trailers, and the low Rotten Tomatoes score, I had really, really, low expectations. Also, having been spoiled somewhat regarding some of the more controversial aspects of the movie, when I finally saw it onscreen it didn't have that same shock value as it might have for others (e.g., Batman using guns or killing).

The parts of the movie I thought were well done:

Aside from his extreme brutality, the Batman parts of the movie were pretty good. The overall darkness of the film suits Batman, but doesn't really work with Superman. Ben Affleck did a good job performing Bruce/Batman. Any shortcomings with the character I attribute to the writing, not the actor.

I thought they nailed Wonder Woman. In much the same way that Burton's Batman helped to overcome the silly 60s version stuck in most people's minds, the BvS incarnation of Wonder Woman does the same for the 70s Lynda Carter version. They convincingly gave us Wonder Woman who is a serious, badass warrior.

The action scenes were pretty good, and they dialed back the "disaster porn" aesthetic from MoS.

Things that didn't work for me:

Please, no more mopey Superman.  Also, I realize that people being suspicious and fearful of a super-powered alien despite his heroic acts is a plausible and realistic response, but to be frank I don't want to see that in a Superman film.  I want to see people look up in awe and embrace him for the symbol of hope that he's supposed to be.  A Superman film is supposed to be fun, escapist entertainment.  I don't need to be reminded about how cynical and suspicious our society actually is -- at least not in this kind of movie.  On this point, Donner got it right.  It might not be the most realistic reaction, but it makes for a better Superman movie.

Lex Luthor was terrible.  Terrible characterization, annoying performance.  He comes off as a neurotic, unbalanced kid instead of a genius super-criminal.  His motivations are not entirely clear in the film either, except that he projects his atheistic tendencies on Superman and has apparent daddy issues.

The movie would have been much better if they hadn't wasted time on scenes setting up Justice League.  The Flash cameo was pointless and added nothing to the plot.  In fact, all the JL cameos were completely unnecessary.  They could have done the same thing with a bit of dialogue at the end of the movie.

They wasted Doomsday by using him for this movie.  When Doomsday was introduced in the comics, I thought it was built up a lot more so that when he finally shows up in Metropolis, you realize what a threat he is and it's totally credible that he could kill Superman.  Before Superman even fights him they spent a couple of issues having other members of the JL getting their asses handed to them.  In this movie he's just another generic movie monster boss character.  You don't get the sense of what's at stake unless you already know who Doomsday is from the comics.  In fact, I think the whole movie relies a little too much on Easter eggs and assumed knowledge.