Nothing is better than a good old fashioned underdog story, especially in regards to combat sports media like boxing (Rocky immediately springs to mind).
What differentiates Blue from others, however is the fascinating premise that our main character Kazuki Nobuto isnt merely an underdog journeyman, he's an arguably BAD boxer (he is 2-10), and yet continues to box purely out of enthusiasm and passion for the sport. He isn't cynical or weary. In fact, he is a positive-thinking kind hearted mentor who seeks to help others whenever possible. Such a premise like this is fantastic, especially when his mediocrity is acknowledged by other characters, and yet Nobuto continues striving to follow his passion with a smile.
Theres just one problem - Nobuto is BARELY the focus of the film. Instead, a lot of the attention is diverted from Nobuto to the secondary character he takes under his wing, who is just the SAME underdog trope character as he is, though slightly different. Unfortunately, a good lot of the runtime focuses on secondary characters who just aren't as interesting, and though their arcs get better slightly as the film goes on, I feel as if it is squandered potential.
Just as important in a boxing film is the choreography of the fight scenes, and though they ARENT terrible, they are not particularly noteworthy, with far too many jump-cuts and a few "movie punches" too many. I'm afraid Creed has set the bar far too high for boxing films regarding their fight scenes.
Overall, not a bad film by any stretch. But I feel like it's incredibly interesting premise isn't used to its fullest potential, and it's fights don't compensate for it.