The DCEU's flaws date back to BvS and are evident in ZSJL. The choice of plot is what made BvS a weak movie, in addition to the worst portrayal of Lex Luthor, Batmans' senseless hatred of Superman and the depiction of Doomsday.
What hurts this movie are similar elements, most prominently, the responsibility of introducing 3 characters, much of the screen time is dedicated to this. Solo outings would have eased the burden considerably.
The story has come too far since MoS, and too soon, so much that everything appears rushed and unearned.
CGI is outright poor, especially Cyborg. In an era where we have had Iron Man and Transformers for over a decade, Cyborg looks out of time. The overall visuals of the movie are extremely underwhelming.
There are also no iconic moments, standout action sequences or takeaway dialogues. Everything feels basic and ordinary.