Batman v Superman wasn't as bad as say Batman & Robin or Steel but it did have some major flaws.

1. Many fans were aware of the Knightmare sequence but it didn't really make sense even with the Flash's involvement. The sequence would have made more sense if Scarecrow had a hand in Batman's terror attacks like for instance his mother's grave bleeding and a man-bat creature popping out. Same thing goes for Superman who was having a dream about his dad.
2. Eisenberg's Luthor was all over the place with no consistency. First, Luthor was calm and composed then impulsive. Luthor would even have episodes of being maniacal or drifting off into levels of dementia.
3. KGBeast had no similarities to his comic book version. No cybernetic limbs or augmentations.
4. Batman is oblivious to Luthor's manipulations and fails to realize the real threat is Lex not Superman.
5. The coincidence that both of our heroes have a mother named Martha was over-played during the fight sequence.
6. Cyborg's origin is loosely explained but hardly interesting.
7. Ezra Miller's portrayal of the Flash resembles the cliche features of a Rasta beach bum.
8. Mercy Graves and Jimmy Olsen are prematurely killed off.

Overall, the movie was used as a marketing technique to get viewers interested about the eventual Justice League movie but the Justice League film could have been marketed the same way as the Avengers. Get our heroes established first with a solo film then bring them together in the Justice League Two-Parter. Due to the mixed and negative reviews, WB is reconsidering Snyder's further involvement with the DCEU and the proposed film slate for the next five years. We can only hope that Wonder Woman and Suicide Squad don't disappoint.