This movie was probably made years ago. Due to politics and infighting within DC, it was not released until now. I feel bad for this movie; if it had been released before Marvel's multiverse phase, it would probably do very well.
It seemed they just threw all action movie tropes into this one. Time travel, multi-verse, old experienced guy teaching new stupid naive guy. Somehow it didn't feel too strange. The movie was still enjoyable. There were a lot of fun one-liners.
The only thing that I wanted to pick on was, there seemed to be no security at the big corporation bio lab, at Bruce Wayne's manor, and at the Russian Siberian prison. Everyone simply walked in. There were guards, but they were more reactionary, not preventative measure.
Aquaman 1, Wonder Woman 1, and Shazam 1 all did very well. But then, Wonder Woman 2 and Shazam 2 were, um, not as impressive. Will The Flash follow their footsteps? Only time can tell.