Each of the 3 episodes are animated and directed by someone different, so I'll go over each episode and what they have to offer.
Additionally, this ONA will probably do nothing for you if you haven't played Kid Icarus: Uprising.
Episode 1: Thanatos Rising (5/10)
Overall, I consider this to be the weakest episode. The story is simple, Thanatos is heading towards a human town and Pit has to stop him with the help of Palutena.
The animation is reminiscent of the 3DS game, and it looks nice. However, the colors are bland and the characters are expressionless the whole time, which makes the 8 minutes a bit
boring to watch. The voice acting is good aside from the awkward delivery, with many pauses and silence in between the lines. There are a couple instances of funny banter and lines, but other than that it's not too interesting unless you've played the game and want to see another story about Pit.
Episode 2: Medusa's Revenge (6.4/10)
This episode, animated by Studio 4°C, has a 2D, storybook-like art style that works very well and looks incredibly good. The story, again, is nothing special but it is a promotional video that shows Palutena and Medusa's rivalry. That's about all there is to it. View this if you like Kid Icarus and appreciate good art.
Episode 3: Palutena's Revolting Dinner (8/10)
This is by far the best episode of the three, being a humorous short story animated by SHAFT. The animation, voice acting, and goofiness are at their peak in this episode. If you are going to watch any of the episodes, let it be this one. The story is a simple slice-of-life and serves as a great supplement to the game. The voice actors are enthusiastic and full of life, as well as the animation being top-notch considering it exists to promote a 3DS game.
If you like Kid Icarus and want to view three more short stories about the world, then this is great for you. Just don't expect a grand story. Palutena's Revolting Dinner definitely takes the spotlight as the best short from this series. It's a mixed bag, but overall, I give this ONA a 6/10.