Alright, so I have seen this movie twice now. Once through my first viewing of the series, and the other through my recent rewatch of the series, after I had read the manga sometime last year. So I can offer both the perspective of someone unfamiliar with the manga, and someone who read it.
I had read the manga purely because this movie left me with far more questions than answers, and a large amount of frustration. Despite claiming to be the finale of the series, and offering closure to your burning questions, it does none of that.
The movie literally begins with the final events leading up to the end of the series, has a few unrelated arcs from the manga in-between, and then skips back to the end without explaining how all of this came to be, or without actually showing the ending to the series. It offers no closure, just questions.
Now then, let's rewind, and see what went wrong.
The one thing I appreciate this "movie" for (which I hardly consider it a movie as it's only 50 minutes long, while the other one is I think an hour thirty) is it made me read the manga.
I now consider the manga and the anime to be two separate entities from each other. The anime is much more comedic in tone, while the manga is more tragic in its narrative (although it also has a lot of comedy). This movie was supposed to be season 3, but that statement was rescinded, and it was decided it was to be a movie.
After some time, and reading the manga, I think I understand the decision, though don't necessarily think it was the right move. You see, the anime by the end of season 2 was already far past being able to accurately follow the manga. Chaos, one of the most tragic characters of the manga series was basically turned into another one of Tomoki's "Angeloid Harem Girls" by the end of the anime. In the manga, she goes rogue after having her heart broken, and kills Hiyori and Astrea, and kidnaps Sugata and takes him to Synapse to start the events that this movie begins with. Problem is they narratively trapped themselves into a corner. Not to mention where the first movie ended was far from the actual ending of the series, which this movie starts with. They had a long way to go, and too many plotlines to fix.
So yeah, I get why they did it, but how they did it is inexcusable. What they should have done is treat the anime separately, and try to end the series in its own way, while roughly following the manga. It could have been done, they didn't need to have Chaos be the instigator for the ending events. Overall I feel this movie, while it does have some good traits, is a totally insufficient end to a great series.
