Perhaps the aggregate score of 30% on RT is a bit low but I wouldn't say the movie was a lot better than 30%. I agree with pretty much everything you said but at the same time, I'm divided. As a fan, all the CGI, seeing Batman, Superman & Wonder Woman was amazing - props for that. But for something that is trying to establish a universe, that's where it falls flat. Most comic book fans are going to watch the films no matter what but for those who didn't read the comics or know very little, it doesn't necessarily make me want more, outside a bunch of cool CGI scenes that had me entertained. I hate to compare it to the MCU but the way Marvel structures and plans the movies is done in a way where I'm waiting for the next one. I'm not saying Marvel movies are all perfect, they're not, but everything just flows and makes sense because they took the time to flesh each character out. We all know why it's Captain America: Civil War, and understand the conflict between Tony Stark and Captain America. Like I said earlier, I think if Marvel released The Avengers and Age of Ultron earlier, it wouldn't get the reception it did because we'd be looking at the characters a lot differently.
If this were a standalone film, Batman vs. Superman, with no involvement in the DCCU, I wouldn't be so critical. It would be just one film that showcases DC's top characters in an epic CGI fest. Gives comic book fans what they want, everyone is happy. But to tell me you're trying to build a whole universe out of this in this format? Doesn't really work.
But with that said, really looking forward to see what Ben Affleck does with Batman. I can't say if he's better than Bale, but I know that the DCCU has a Batman that everyone can lookforward to.