I'd just like to start by stating: This is a direct sequel to Brave, which is itself a direct sequel to Dan. I can guarantee that the enjoyment of someone who hasn't seen the 2 prior series would be limited. After having watched Dan and Brave, I heard of Saga Brave, and wondered how they could add to the story. Well, this was a perfect closure for the series. It revisits the most important characters from Dan and Brave, and how they adapted to society after the events of those series. As a series all it's own, it still has it's own plot. It's not verydevelopped, as expected for 3 episodes of 20 minutes, which revisit prior characters, and include a card game in each. But it serves it's purpose well, and ties everything together nicely. If plot=story, I'd give it a 7.
I can't comment much on art or music, but I can say that animation wasn't bad at all, and that the soundtrack didn't stand out much. I'd give 9 for animation and 8 for sound, but anyone could argue that they deserve somewhere between 5 and 8, and I wouldn't disagree.
The new characters don't do much, and the older character don't develop much. However, since there's a time skip between Brave and Saga Brave, we see how they changed to live in the new society. If this was to review the characters as established in the previous series, I'd give between 7 and 8. But with what Saga explores, I give a 10.
I'm rating a 10 out of enjoyment. I was annoyed that the new planewalkers and saga brave (as a game mechanic) weren't explained at all, but this series was so interesting that I looked it up afterwards. I was happy the whole watch through.

Overall, I believe this series to rate a 9 out of 10. I would assume the low rating are either from people that didn't watch the prequel, or would have preferred a status quo to the world after Brave.
Or maybe I was just so overjoyed to come back to this series after the dissapointments of Zero and Burning Soul.