Friend of mine bought Kingsglaive and gave it to me for free so I watched it too.
Non spoilerous opinion:
I don't know why it got criticized, it's a pretty good fantasy film even if you don't know anything about FF15. Obviously if you want to know what happens next you have to play the game, but it's a good prequel and good standalone fantasy.
And SE really doesn't go cheap on graphics, pretty great in that aspect.