So, in their attempt to keep up with Marvel, having only three heroes most people have heard of, the DCEU fall back on The Flash, who can...run incredibly fast. This apparently means he can reach such a velocity that he can breach the barrier between alternate universes and try to undo the death of his mother. Naturally the butterfly effect of trying to alter time comes into play, and whatever he or his younger version in the alternate universe try to do to change events is cancelled by the halfheartedly explained immutable timeline, or somesuch.
To the film's credit, it is made clear that the hero hasn't got a clue about consequences either, and despite the usual overabundance of digitally-animated action and fight sequences, it is actually quite good fun, bringing together multiple versions of Batman from over the years to assist the hero (principally Michael Keaton reprising an older Batman from Tim Burton's films) and incorporating numerous other nods to genre fans.
But they shouldn't take this as the way to go in the DCEU. Marvel have already tried quite a few times, and it's not a pony with many tricks.
6/10