It's not that complex. Or, complicated.
Morrison has admitted that it confused or annoyed some readers, yeah, but it sold and sells really well, and continues to be in print.
It's just a superhero comic.
It's in no way "mainly about Grant Morrison's previous work." It's not even significantly about that.
It's mainly about horrible old gods (who represent bad things in our lives and world) temporarily winning, and how the good guys turned that around. Because that's the plot. The villain is less punchable than usual, but it's still a straight up superhero comic. Folks in flashy costumes with mad powers being heroic and just and cool and beating horrible monsters before they can destroy us.
It's okeh to be disappointed in it. It's okeh to dislike it. Or, love it. But, it's no good overselling it as super-complex and unknowable or some big "it's only about Morrison/about comics" treatise. You know?