TL;DR If you're thinking of watching it then go for it, no reason not to. It's basically exactly what you'd expect. Movie was quite boring but really picked up with the final fight which makes sitting through the entire thing worth it. Review will have light spoilers (Marked).

If you're reading this review chances are you have watched the TV show. I knew exactly what to expect going into this movie: Great fight animation, fantastic score, a generic plot that allows to set up the fantastic moments and apparently some emotional sequences. I was not expecting anything that would be incredibly thought-provoking or something that'll keep me awake at night looking through my brain for answers, and it's exactly as expected.

The enjoyment factor in this movie comes from it's animation, music and supposedly from the characters.

Animation: Again, nothing more than what I'd expected. In fact, I'd say I was expecting more, but that's only because I re-watched the Heaven's feel trilogy recently and anything that's not beyond a masterpiece looks inferior to it. The CGI looks good; the shading is great but the movements are quite, well, CGI-like. Nothing that would redact from the experience, unless you're a huge animation nerd like I am, and even I didn't care much about it because I was too busy looking at the good stuff.

THE GOOD STUFF: (THE VIDEO IS A MAJOR SPOILER)

50 seconds of uninterrupted Nozomu Abe sakuga. This has surpassed his work in episode 19 and is now my second favourite cut by him, coming after only the climactic scene from fate heaven's feel 2. It's so exceptionally well detailed and is perfectly complemented by the genius of Yuiichi Terao who leads the compositing and digital team that it made me tear up. It wasn't just this scene however; the entirety of the final battle was pure bliss. Heaven's feel's climactic fights were about who can make the larger explosion, so it was very refreshing to see a martial arts based well choreographed scene from Ufotable's staff. It wasn't just Abe obviously, Masayuki Kunihiro did some amazing cuts, and even freelancers like Hironori Tanaka joined in. The final fight is amazing. I can't say it enough. I'd say it's in the top 20 fights I've seen in all of anime; I've watched a lot of anime fights.

Things that lowered my enjoyment:

1) Characters: There wasn't really enough time to get attached to Rengoku, so the emotional scenes just didn't hit me as hard. Even though I'm an extreme cry baby (I cried when I first watched deku vs muscular) I didn't even tear up here. It was basically: "Show backstory, show epic scene. Now cry". It worked on my sister but that was mostly because she instantly fell in love with his character because he has Daichi's voice who (Haikyuu! spoiler) ~~tragically dies in season 2~~, so she had that emotional attachment from the get-go.
2) Plot: I've seen it a million times. It's basically a rip off of infinite tsukuyomi from naruto, which in itself is a rip off of the rip off of the rip off of the rip off .....(n times). So yeah, it's gotten a bit stale.

Not the anime's fault:

1) All of the damn spoilers (spoiler...duh): They might as well put Akaza on the cover at this point. It was the only real plot twist in the movie and it didn't come as a surprise to me. what did surprise me though is his banger theme. Very noice.
2) Viewing conditions: Half the experience is in watching this movie in a movie theatre. I couldn't even imagine. I surely would have whipped my nichirin sword out to rub out a few breathing techniques if I viewed it on a big screen. Unfortunately I didn't get to do this. Around 50 thousand votes on change.org, which was enough for tenki no ko, wasn't enough to bring mugen train to India so I could not watch it in theatres.

That's pretty much everything.