Not a fan, personally. You say it's a good movie with its own message. If that was true, they would have just called it "Advent Children", and not "FFVII: Advent Children".

If you remove the FFVII connection from the movie, does it still hold up? If the answer is "yes", then that's what they should have done.

The movie ruins most of FFVII's story. Sephiroth is dead. He's ultra dead, having both his body and his mind torn to shreds by the Heroes at the end. It's the whole point of the final battle.

The life stream is the life energy of all living things. Once you're absorbed into it, you're done. "Don't worry, he's part of the lifestream/planet now". Not "don't worry, he'll reincarnate as long as he really, really wants to". That doesn't happen. If it did, Sephiroth would sure as hell not be the first person of the trillions throughout the Planet's history (or vastly more, since this cycle takes place across the universe and is known by the spacefaring Cetra) to hold together after being absorbed.

The movie cheapens the entire story of the game, pulls powers, characters, and plot elements out of nowhere, and largely exists just to give fans a big flashy fight scene between Square's ultra depressed Cloud (as opposed to the one we actually see in the game) and his arch nemesis, the broody "best villain of all time", which just means he can't ever die.

But, hey, if you want a stupid mindless action flick between FF styled characters, go for it. It's a decent watch from that angle.