Oh, where to begin.
Well, Kingsglaive: Final Fantasy XV is not a totally bad movie. But it's not a great one either. There's a lot of things that I liked and plenty I wasn't a fan of. I'll just break it down.
First off, I like the story. It brings me back to the modern medieval knight feel that I love in Final Fantasy VIII. The pacing, however, leaves much to be desired. There wasn't a moment where there were reactions in the theatre because barely anyone knew what was going on. The action was too fast and the slower scenes did not last long enough. Seems Takeshi Nozue went to the school of Michael Bay directing because although there were a lot of neat scenes in the movie, they were zoomed in too much and went by so quickly I could barely figure out what the heck was going on.
The animation was... blech. If you're going to do a 3D animation, then ANIMATE IT. Don't just motion capture the crap out of it. Motion capture is okay for slow movements, but it doesn't do well for fast movements and expressions. Advent Children looked great because the team treated it like an animation and not a synthesized live-action film. Why is there a need for detailed realism when you made the choice to animate it? Just look at the skin texture for one of the original trailers for the first version of the game and compare it to a Kingsglaive trailer. If you want realism, then just make the movie a live-action. At least it'll look decent rather than synthetic and sterile.
Opening narration by Lunafreya was a complete waste of time because all that were easily explained by the rest of the movie. The first rule my script-writing teacher taught us was to SHOW, NOT TELL. Otherwise you risk losing the audience by bombarding them with too much information a la Star Wars-style. If you can't pull your audience into the story without having to straight up explain things, then perhaps the direction of the movie should be reevaluated. The first 3 or so minutes should've just showed Regis and Noctis visiting Tenebrae and getting attacked by Niflheim, which could then transition into the battle scene where the characters later talk about the formation of the Kingsglaive.
Nyx and the other characters in the movie feel like they'd be really great characters, but the frantic pacing of the movie took a toll on their development. It makes me wonder why they didn't just commission the whole story to be part of the Brotherhood anime instead as I believe their character development would benefit greatly from a more drawn-out presentation.
(Personally, I prefer Stella from the original version of the game over Lunafreya as Lunafreya feels like a watered-down version of the character that used to be Stella.)
The fight scenes are where the movie really suffers. Tetsuya Nomura did a great job presenting fast-paced fight scenes in Advent Children while still showing enough for the audience to understand what the heck is going on. Takeshi Nozue unfortunately fell flat on this for Kingsglaive as the fight scenes were all quick flashes. It's a real shame because it looks like there were some great fight scenes in the movie; I just couldn't see what was happening. :\ I dunno, maybe it's better viewed on a smaller screen than a big screen. But I was still able to get a handle on what was going on in Advent Children compared to Kingsglaive on the big screen.
A big complaint about Spirits Within and Advent Children was that there weren't enough Final Fantasy monsters being showcased (or any at all). The Kingsglaive team did well to incorporate them into the movie, but again, the effort goes unappreciated because we don't get much of a good look at them. There were the Niflheim demons looking like Diamond WEAPON from Final Fantasy VII, Ultros on the airship, and the recognizable Behemoth monsters. (I initially thought the monster on the airship was Malboro, until I saw the tentacles. Seriously, stop zooming in and showing glimpses!) I do feel happy that there will be summons in Final Fantasy XV as I saw Odin, Yojimbo, and possibly Shiva make appearances in the movie. (Still needs actual Chocobos, darn it!)
Overall, I feel Kingsglaive suffered from the opposite condition of the Star Wars prequels: too much going on, not enough drawn-out scenes. It honestly screams "rush job" and I do hope they give the movie the Advent Children treatment and redo it. I feel it has potential, it's just being buried under explosions and glimpses. I am kind of worried that the game will be a glorified Sword Art Online because the story makes it seem like only those related to royalty are allowed to use the power of the crystal. Surely magic should be more accessible to people to provide healing roles and alternative police forces that use magic.