Just watched it on Netflix. Wow, the nostalgia! I wasn't expecting Miyagi's backstory, but to be honest, it turned out really well and gave me goosebumps several times, especially during the scene after they won when Miyagi looked up.
However, I was kind of expecting other details from the original series that sadly weren't included. For example: Rukawa's flashback with Sendo (where Sendo tells him the name of the player he couldn't beat – it was Sawakita, but he scrambled the name) and the double-team by Rukawa and Sakuragi on Sawakita, where Sakuragi steals the ball. I expected those moments to be emphasized more.
But still, it was a great movie nonetheless. Kudos to everyone who made this possible. 9/10 for me.