So this is perfect time to show why Rotten Tomatoes is preferred by Hollywood as an aggregator here is it on Metacritic
Justice League 56
Positive 12
Mixed 18
Negative 4
RT turns most of those mixed rating into positive rating, because it is at its heart RT is a Pass/Fail system. So while people are out here being mad at RT, It actually protects movies which is why you don't see grumpy Hollywood types saying go to Metacritic. So for more clarity it is something like this
Positive goes from 100- 67
Mixed goes from 60 -40
Negative goes 38 and below
These are reviews from major sites, News papers and film outlets as well. So as you can see most most reviewers have it as mixed or 60%. Which puts a better framing on this topic it is okay to like an average movie. As much fun as to talk about it that way it isn't just Good or Bad. And that is biggest problem with RT system imo.