My points have already been mentioned, but...
Initially I was worried when Snyder was hired. He seemed to be the only one who wanted the job, and the only movie I liked of his prior to Man of Steel was Dawn of the Dead. Then Man of Steel turned out well (for me). Throw out Pa Kent (even though I really like Costner) and redo the last fight and you've got a great film. But you know, Superman was back and they'll hit it out of the park with the next one...
We have to add Batman? Really Warners? Wonder Woman? Ok, that'll be cool to finally see. I really just would've liked Man of Steel 2 though.
Then sometime shortly before BvS, I read that article about the supposed reaction at Warners not being good. Mix that with all the commercials and trailers showing the same footage again over and over. Remember, if the advertising shows the same thing over and over again, nine times out of ten that movie is garbage.
As a Superman fan first and Batman fan second, I also wasn't a big fan of the shot in all of the advertising with Batman stopping Superman's punch. I understand why that's there, but as a character after Man of Steel, Superman was hardly on his own two feet in the public eye. He was back but not triumphantly. It felt more like Warners was like, "Hey, you all love Batman right? Now watch him kick Superman's ass!" instead of propping both of them up. I know it's a versus movie, but it was also supposed to be a sequel to Man of Steel (in hindsight, that's a load of ****...Superman has what, 42 lines in the theatrical version?).
Then they just flat out revealed Doomsday. Smarrrrrrrt.
Then the movie came out and for all I cared they could've burned that universe to the ground right then and there. That's when it failed (the first time...we still have at least two more movies).
I'm glad they ultimately didn't burn it to the ground because we eventually got Wonder Woman and a watchable (for me) Justice League, but of course we had to go through Suicide Squad first which is only marginally better than BvS.