****SPOILERS****
It was a fantastic movie, though DC does need some work on their creative direction and CGI coordination. I appreciated the comic-book cell appearance of multiverses, but the colliding globes of mixed stills and motion was a bit undefined and seemed rushed.
I see and hear many complaints about the concept of the multiverse and multiple versions of characters from Marvel fan-chads. The concept of the multiverse is old. DC, Doctor Who, Star Trek, Alfred ** Hour, Twilight Zone, fiction novels - multiple franchises have been using that concept for ages. This isn't some new concept novel only to Marvel and any other franchise is just copying. Same goes for different versions of characters. The concept is part of the multiverse. Superboy Prime, Wonder Woman, FLASH OF TWO WORLDS (1961)... Just stop with the fanboy stuff.
The plot and ending make sense, which was explained wonderfully by Bruce Wayne (Keaton) in the movie. When the diverging decision is made, the timelines intersect at that moment rather than split. So you end up with different pasts as well as futures. It's rather foreshadowing as well. Because Barry's mother died, he was in the lab when the lightning hit, thus granting him powers to be able to help save the universe. But because he went back and saved his mother, he wasn't going to be there, instead on a date. Barry interferes again, but like the bowl of spaghetti, the decision parallels rather than splits the timeline. Survival depended upon the conditions of the past of his time. All that's different now. So the destruction of the world is predetermined and unavoidable. Doctor Who fans would call this a "fixed moment in time."
The characters were excellent. I really enjoyed the juxtaposition between straight arrow Barry and stoner Barry and the enlightenment it gave the former. I feel like the character grew through the experience and really matured in many respects. The sprinkle of jokes and character flares gave us plenty of laughs. Rope of Truth, the presentation of the babies, Barry 2's childish behavior with his new-found powers. As a whole, the characters were very enjoyable. Though the young Barry and parents' relationships wasn't convincing. It just felt way too phantasmal.
The fight was a lot of fun to watch, and the static discharge was a neat way to solve a problem. The "put your hands together" to ground yourself was a bit odd but makes some sense. With a single path of electricity and the target grounded, the path of least resistance is THROUGH the Kryptonian to the ground. But with two directions of current on such a small target, some of the electricity can come back to the source when the combined currents discharge. Electro-bender engage.
The villains were good for the most part, but I think DC could have done more with their appearance. I would have also liked to have seen more of General Zod. They could have also done more with their CGI creative direction. The globes of alternate timelines looked cheesy and the chronobowl was just plain dumb. A hamster ball to navigate time? Why not have Barry absorbed into the dimension to navigate time, and when he emerges, he leaves a tiny piece of himself behind. That mechanic would also explain the implied degradation of future Barry2. But that transformation isn't explained at all either literally or in proposed theory in the movie. It's just "here's future Barry2 that's been poked so many times he looks weird." It would have been great to see more of future Barry2 as well.
I feel like DC did some great work in a lot of areas to deliver a good movie, but their shortfalls kept it from being "great."