I don't know. I wasn't thrilled with Justice League 6, but I'm trying to remember that this is supposed to be the first encounter: Darkseid doesn't see this level of resistance coming and so is unprepared. Final Crisis, Rock of Ages, etc. are all in the future. The first encounter can't be as brutal as the later ones, nor can it be as epic. Am I satisfied woth that? Not entirely, but it's at least understandable.
Some splash pages are better than others: Wonder Woman's sheer exhilaration as she stabs Darkseid in the eye is tremendous, the double-page of Superman isn't aesthetically all that pleasing.
The back-up story was more interesting. Does this mean the Phantom Stranger's angelic origins are gone? Did we just get a big clue that the New 52 wasn't supposed to happen? If so, is the conflict with Darkseid rather than Starro the Conqueror an acceleration of events? I mean that Starro is or was good practoce for the League before they faced Despero et al., and Darkseid eventually. Without that "practice", was this victory really just luck and we're all in for it later?