I put off watching this after enjoying season one because of a poor revie here. I disagree with that review whole-heartedly, so here's my first review after being on this site for years!
If you have not seen Season 1, you should go watch that first. This would make little to no sense without knowing all the characters and history from Season 1. Check out the reviews there if you want to learn more.
If you have seen Season 1, here's what you should know about these 3 OVA. Our main characters attend an "All stars exhibition". The categories of events they don in the competion are a little contrived, ok very contrived. However these plot devices do give a valid excuse for all the characters you know to be in the same place at the same time, and to allow for some interesting encounters. Mostly these OVAs are going to feature a few characters dualing in exhibition matches, while everyone else in the stadium gets to enjoy a holographic display of the match.
As someone who enjoyed Season 1 of this show, I was pleasantly surprised at the quality and happy to scratch this itch while waiting for Season 2. As with Season 1, i think the animation is pretty incredible, the characters are enjoyable, but the plot isn't terribly deep or complex, just fun.