The world building in this short film is spot on (Well mostly). It shows that the makers of this short story were a big fan of the Wizarding world (despite being muggles.).
The characterization of James, Sirius, Remus and especially Peter was more closer to the books than they were to the WB movies. And it was good for a change (I know you want to know what was Snape like, I'll get to him.).
It fills a little gap between, Their graduation and eventual death (Can't believe all of them will die before Voldemort.). It gives context, to the world. And how they came to be, what they came to be. It provides a little closure for those seeking into the past of The Half-blood prince.
It mostly rest the arguments between potterheads of what and why they did, what they did in their future. Snape specially.
If this is cannon, then I could relate to why Snape was a special case for James, as Sirius said in the books. He was his biggest rival for Lily, and he somehow still internally feels that he has forced or nudged her choice in his side, unfairly. In all the four maurauders I always liked Remus the most, He wast the most sensible one in all of them (BTW, He also had a little crush on Lily). Peter is Peter, Squeaking away like he always did, and since they are recent graduates they all still are a little novice when it comes to spells and casting. I was a liitle shocked by the characterization of Sirius, In here he is just a little blank slate. He has no opinion of his own, and just follows James wherever he goes.
Now coming to the star of the show, Snape. Man I knew he was a little OP, but still. In the books Sirius at one point states that In first year he knew more spells than half the final years students of Hogwarts. In his sixth year he made several spells of his own, One of them is quite deadly. He was an expert in potions and also was a member of Horace Slughorn's club with James and Lily (Though Lily was in the club because of Snape.). He dueled Minerva, flitwick and harry all at the same time with retaliating once and knocking out Carrows.
Hang on wait a second, this guy is literally OP. Scratch what I previously said, the characterization of Snape is also spot on. Dueling all the maurauders at the same time. It was spectacular seeing him take them down, Though Vfx and the duel itself could have been a little better and agile. The short film portrays the inner struggles of Snape of being a good guy or a slytherin (No matter what you say, all slytherin are bad. Ravenclaw for life.).
In school he never retaliated to his bully because of Lily, because she didn't wanted him to be like James. And despite hating it, he loved her, respected her and therefore only endured what came on him. Except for that one time. And for that godforsaken one, single, time, he paid for with his entire life. His soul even. Being judged as a bad guy when all along there was no one better than him. As Harry said, He is the bravest man in the series.
I will not drag it more with this review cause it's already a little long.
All I will say is, If you are a potterhead then you owe it to yourself to see it, despite what you believe about the characters of the world. You'll get a more in depth look, of their mind and the force behind their actions.
Ravenclaw for life.