The DC Cinematic Universe should be studied. Without comparing it to MCU, which DC is trying to echo, it's just a mess with both too much and too little connecting tissue that as a shared universe is all over the place. You then have films like 'Joker' and 'The Batman', which exist outside the cinematic universe and leave audiences even more confused. They were trying to get 'Justice League' off the ground but built little groundwork unlike 'The Avengers'. The films were also objectively bad, and then you have the real-world reshuffling of films and the hiring of James Gunn to steer the ship. Then films like 'Black Adam' and 'Shazam! Fury of the Gods', which in the grand scheme of things are just roadblocks because they don't fit into the grander universe, and are also nothing special. But the most interesting of these limbo films, existing between the old universe and the new, is 'The Flash' - and that's not just because of its lead actor.
SWITCH: 'THE FLASH' FINAL TRAILER
After the events of 'Justice League', Barry Allen (Ezra Miller, 'Fantastic Beasts: The Secrets of Dumbledore', 'Trainwreck') A.K.A. The Flash is unsure of his role as a superhero, which leads him to reflect on his past. Still processing the loss of his mother (Maribel Verdú, Netflix's 'Élite'), which in turn sent his father (Ron Livingston, 'Tully', 'The 5th Wave') to prison, he tries to go back in time and stop this. After successfully pulling this off he gets trapped in a universe with no metahumans so it's under attack from General Zod (Michael Shannon, 'Amsterdam', 'Bullet Train'). Once there, he finds that universe's Barry (also Miller), who is yet to become The Flash, a different version of Batman (Michael Keaton, 'Spider-Man: Homecoming', 'Birdman') who has retired, and Supergirl (Sasha Calle, TV's 'The Young and the Restless'). Together they try to stop Zod while also working out how to send Barry back.
Compared to most of the DC slate - sure, this would rank higher than most, but it's nothing extremely earth-shattering.
My groundbreaking verdict: this movie is completely adequate. Compared to most of the DC slate - sure, this would rank higher than most, but it's nothing extremely earth-shattering. The effects are still bad, the villains are still weak (which considering he is returning is wild) and the third act is messy. It's the same DC problems in a slightly tighter package.
Let's talk about the lead. I never liked their version of 'The Flash' in 'Justice League', and while it's better here it's still a version of the character I don't quite connect with. You have to top that off with what they're accused of having done in real life, and that just makes me uncomfortable. We also have them playing two versions of the character and the second version is meant to be stupid and nothing more than overly happy comic relief, which at times becomes incredibly annoying. No matter how much the movie tries, reality is sitting there in the back of your head, and then you have the fact that this version of the character isn't the best portrayal so it's hard to get behind.
The movie is also more focused on Keaton's return, and while it's exciting to see him back in the suit the film doesn't have much for him to do. While the story on paper has heart it doesn't completely land on screen, partly due to the lead. The action also isn't very memorable, while in terms of effects it's better the sequences themselves aren't that exciting, even with Batman.
'The Flash' is nowhere near the bottom of the superhero barrel - even for DC - but when you mix in the real-world drama and the mediocre film there isn't much to rave about. As an entry in the confusing DCEU, it will go down as a respectable venture, but where it's been released in the timeline is only going to baffle audiences further as the new films come.