Honestly, i don't know why there are some many 7s or even 8s. This OVA is just one adaptation of one of the sidequest you can do in the game source (and a uninteresting one in my opinion). As a stand alone product it fails because you need to have played to game to understand it and as content for the players it's pretty boring because it focus too much on irrelevant characters and tries too hard to make the heroes looks cool without them doing anything remarkable until the only (and final) battle. By the way, the ending doesn't make any sense at all, what was the point of that scene? Nothing, just a crazy reference out of nowhere.
The animation is good (the baton pass is probably the highlight), nothing more than a few fails here and there but it's good overall. The music is hard to tell, it fits but at the same time it's weird to see the music from a game in an animation. The new characteres are boring, nothing more than archetypes and the "villain" is just an edgelord. I still could find enjoyment watching this because I played the game, but that's not an excuse for the product to be so mediocre in content. If you can only make an OVA and it's for fans of the game you can adapt one of the most popular moments of the game or do a quick introduction with an original history.
Actually, i don't know why did I expect something more than mediocre from an anime based on a videogame.