Let's be honest here, I was not looking forward to see this movie. But, since I ended up seeing it, let me shed my personal grievances with you. And yes, there are spoilers!
The whole story premise SUCKED! The idea of having the protagonist go back in time to fix a mistake only for it to cause more mistakes is not new. Flash however turned that concept on its head. Instead of just changing the future, he changed the entire timeline. As far as science is concerned, time is considered linear, with any possible alternate universes running parallel to each other. in the case of a comic book series, there were things of canon events, which apparently connected each iteration together with defining points in their lives. For Flash, it defined time as pretty much a big jumbled mess of realities, where even the slightest deviation from a different universe causes another reality to join the cesspool.
Generally, I hate the ideas of fate, predetermined destiny, and multiple realities. Aside from that, there was plenty more wrong. The alternate Barry was used as comic relief, which in my opinion are some of the worst characters in a story. The action sequences were not even thrilling. Generally, I knew this film was a terrible flop the first time I saw the trailer. If you like it, thats your choice. But as for me, I hated it through and through.