I actually quite enjoyed the film as well. For me, it was better than the original Flashpoint comic it was based on (and the animated Flashpoint film) because the comic had to spend time on Barry/Flash, Reverse Flash, and the Flashpoint/alternate timeline versions of Batman, Shazam, Cyborg, Superman, Aquaman, and Wonder Woman, and all in only five issues, it was too much*.
The film wisely keeps the focus on just Barry (and Barry), Batman, and Supergirl (with quick cameos by a few others), and thus feels like a tighter narrative with more room for character exploration.
*I think a likely reason the comic tried to do much is originally Flashpoint was just a Flash story where he changes the timeline, learns his mistake, and fixes it. But after the story was announced to be coming up, DC was bought under a new owner, and editor-in-chief Dan Didio felt pressured to do something to impress the new owner, and so decided to reboot the comics continuity and use the Flashpoint story to do so (as Barry’s attempt to fix his mistake at the end of it causes a reboot instead).
So they probably ended up adding more characters than originally planned since the story was suddenly made to be the end of the existing DC comics universe (it would be brought back five years later, needless to say longtime readers did not appreciate so many developed characters getting the reset button) rather than just a Flash story.
I will say though, while I loved seeing Keaton as Bruce/Batman again, in the Flashpoint comic, the alternate timeline is revealed to have one of its differences be it was BRUCE who was shot and killed by Joe Chill, and Thomas and Martha Wayne were the ones who survived that night. Thomas is who becomes Batman, and Martha loses her mind in grief over the loss of her son and becomes this timeline’s Joker. The Batman v Superman movie features a brief flashback of the Waynes’ murder with Jeffrey Dean Morgan playing Thomas and Lauren Cohan playing Martha, two noteworthy performers especially given their recent Walking Dead roles, so it seemed they were planning on doing the Flashpoint versions of Thomas/Batman and Martha/Joker at some point thus why they had such noteworthy performers playing the roles so briefly prior, but changed their mind by the time they began working on the Flash movie.
