No spoilers, just opinions :D
I really enjoyed watching the original Date A live when it first aired. The second season was not as good but this film, Mayuri Judgment, just disappointing to me. Being that the original Date A Live aired a couple years back I was probably less aggressive towards the cliches of this series, but watching this film now has made me wonder why I ever enjoyed Date A Live; has it always been like this?
The story takes place after the events of Date A Live II so all the previous characters will appear in this film. The new character(s) is developed poorly for a 2 hour movie. The art is the same tier as the previous series so no complaints there. It has a bit of "service" for the fans of each girl in the series. Finally, it pulls a completely fresh plot that forces action scenes and juggles it around with a dash of bad pacing.
Why is it the highest rated in MAL out of the Date A Live series? I'm not sure. Do I recommend it? Nope. Unless you must see more Date A Live. I personally think Date A Live II concluded fine without the movie. 4/10 on my book.