To be fair, Empire Strikes Back had initially mixed reviews as well, and was only highly appreciated after Return of the Jedi was released, and it was viewed as part of the whole story. A lot of fans were confused and disappointed by the darker tone of the whole movie, and it's ending. This will likely be the same, though as I've said, there are some fans who are literally impossible to please at this point, and that's ok. The movie is doing well at the box office both in the US and overseas, so I think the vocal minority of audience reviewers are making themselves extra loud. Only time will tell if it gets better with age, as Empire did, or not.
“Eternity is a terrible thought. I mean, where's it going to end?”
― Tom Stoppard, Rosencrantz and Guildenstern Are Dead
― Tom Stoppard, Rosencrantz and Guildenstern Are Dead