Batman v. Superman is a good movie. If you don't like comic book movies you'll get little out of it, but it follows Man of Steel in bringing a more mature tone to the genre and carries on that movie's strengths.
What it really did well was the slow burn through the first two acts–the story was unusually good at ratcheting up the tension and conflict with shocks and escalation until the big fight between the two main characters. It really felt like the conflict expressed the natures of the characters and was not some contrived misunderstanding.
Eisenberg was surprisingly effective as a more manic, psychotic version of Lex Luthor. His obsession with gods and monsters was an interesting development of a villain who in the comics was either a pointlessly antagonistic super-genius or, later, a fat corporate titan. I wasn't convinced Eisenberg could pull it off, based on the trailers, but the movie would have definitely been worse off without him.
Affleck as Batman was smoldering with resentments and insecurities. This aspect of his character came out more here than in the Christopher Nolan movies. It was a good direction to take the character in, seeming both fresh and well-suited to the more realistic and darker setting of Warner's Man of Steel universe.
If the movie has any faults they are in the third act, where the Doomsday fight was anticlimactic after the Batman v. Superman main event (the latter was, despite the grumpy reviews, as well-choreographed as the tremendously fun super-battles in Man of Steel). It doesn't work because the Doomsday character–really just a mindless transformation of General Zod–isn't very well-defined so the fight against him lacks tension. As TEO wrote, it's just an excuse to feature the three superheroes teaming up. And coming after a climax that had plenty of emotional stakes, it played out like something slapped on from a lesser movie.
The Justice League teasing is a fairly minor part of the movie; it didn't seem particularly well thought-out and mainly consisted of characters browsing video clips of the minor league superheroes to come (pretty lazy writing, actually). Wonder Woman herself probably should have been left out of the final conflict–she was more interesting as the slightly mysterioso art collector.
The real chemistry in the movie is between Affleck and Cavill, which points up how well-cast Affleck was despite the initial fan furor. Cavill still feels like he is working out the kinks of a character who is nearly a god, but when given the right lines is good at indicating that his character is not sure he wants to be one.
All in all, a pretty smart script where it counted, and a third act that if you cut it off shortly after the mano-a-mano would have been just about perfect. The only thing dampening the mood was the urge to keep adding on unnecessarily, plus a shameless cliffhanger epilogue that tries to reproduce the worst sort of event comic gimmickry. It felt like Warner was so anxious to get its Justice League dick out of its pants that it forgot it was still in the middle of its first date.