We get so much more context about Africa and why it happens how it does (also a bonus scene of Lois Lane randomly being a dick to Jimmy Olsen for daring to introduce himself)
Superman helps the bombing victims before he disappears, and Anatoly the Russian proves to be a first rate evil henchman, pulling off two murders and two abductions flawlessly, plus making a killing spree in Africa look like Superman. Seriously, If I ever put together an evil plan, I'm hiring that guy. We also get why the government guy won't go on the record, because that involves revealing that the CIA were about to bomb a village full of innocents (but in a nice bit of grey, the team they had on the ground were against the move.)
A lot of nice details I never noticed the first time, like how Bruce turns around the MMA fight by whispering in that guy's ear.
The actual BVS fight was better than I remembered, although I still don't think that was the Bat fighting at his best. Neither was Supes, but that's forgivable as he has no idea Kryptonite exists yet, so he thinks he has no need to go all out. There are a lot of things lifted from The Dark Knight Returns, but some of the really important stuff that made things work in that comic was left out.
We get Lois Lane and the Senator figuring out Lex's plan, making everyone look better as he had to work to keep them silent.
Great action (mostly), great soundtrack.
Weakest points for me as a fan of the Bat was that needlessly murder-filled car chase. You could argue that they're entitled to their own interpretation, but in the same universe where the death of Zod was such a big deal, you can't just go 'oh, yeah, he kills people now.' The only thing they had that was actually a threat to him was that one heavy gun, so it was unnecessary even if he didn't already have the truck tracked.
Other weak point was of course 'MARTHA', but on a rewatch it isn't as weak as it looks. Bat's first response is confusion/anger, he thinks it's some kind of taunt or threat, then when it gets explained he has a flashback to the loss of his own Mom. I'm not going to say that was well done or anything, but it's not the horrible mess the internet thinks it is.