Introduction
This is my first character review for Overwatch. To truly be able to "review" a character for Overwatch is to play as them for at least 12 hours and after clocking in 19 hours as D.Va, I think she is a good candidate.
I would also like to let everyone know that this is my first review, completely unbiased. I will review the character based on their story, gameplay, design, and how hard the character is to defeat. Then give a score from 1-10 for each category. I will give a general idea of each category, and may omit some stuff out of it. I will also include a fact for each category.
Story
D.Va (Hana Song) is a former professional gamer, who uses her gaming skills to pilot a Meka (mech) to defend her country, South Korea. Which, is very effective. She is really competitive, she will do anything to win. 
Nothing was going right back at her home country, however. A MEKA could not defend against an omnic that attacked her nation. The omnic, which continually adapts, disrupted the MEKA's drone networks. Which forced the military of South Korea to put pilots into mechs. They decided to find suitable candidates, which were professional gamers. The government did this because of the gamers reflexes to operate the mechs. Many professional gamers were drafted, including Hana Song (D.Va). Stepping out of the spotlight, she decided to get an armored mech operator license. Being a part of MEKA, she gets to use her skills in the real world instead of the video game world. Her skills and competitiveness make her an extremely competitive pilot. Overall, she is a great character thus far story-wise. While her story isn't sad like other characters from Overwatch, people around the world look up to her. Even in South Korea, her character was used as a symbol for the feminist group "National D.Va Association." Which, is for feminists that are fans of Overwatch. Her story is therefore inspirational to others, especially women. 
Also, D.Va's story doesn't feel like it goes in-depth as with other character's stories. Such as Reaper or Tracer. I think Blizzard may update her story in the future. But as of now, there isn't much besides that.
Rating: 8.5/10
Gameplay
Admittingly, D.Va is fun to play as, she is a tank character. You can use fusion canons, which is high-fire twin shotguns. There is also her defense matrix, which shoots down enemy projectiles. Both of these are good for close combat. She also has her boosters, which launches her into the air. This one is good for an aggressive playstyle, which could be considered by flying in the enemies face while shooting projectiles at them, such as micro missiles and the fusion canons. Her ultimate ability is self-destruct. When you activate this, she starts a self-destruct sequence and launches out of her mech. Then, the mech explodes and kills any enemy in explosion's path. She can instantly call forth another mech at max health. She also launches out of her mech when you lose HP, which can add an extra annoyance to the enemy team. Which, after taking damage or hitting/killing enemies with the light gun (which is a surprisingly effective gun on its own) you can call a mech again.
While she does have useful abilities and can be hard to kill in her mech, she can easily die out of her mech. Which might be a trade-off Blizzard did to balance the game, but when you're in the middle of combat, it is very hard to not get killed by an enemy while out of mech.
Rating: 9/10
Design
I have to admit, her design is pretty awesome. Her mech is entirely pink while having an array of "sponsorships" all over her mech. I think Blizzard did an awesome job with this. The design of D.Va (Hana Song) is pretty good, too. She wears headphones, which is reminiscent of gamers wearing headphones with a mic. She also has war paint on her cheeks, which does show how serious she is. She also wears a suit, with a bunnyhop logo around her neck (bunnyhop is the name of her mech). Overwatch went with a cartoon-style with designing their characters in Overwatch, and I have to say it works out pretty well. They also have an array of skins and emotes. Which helps make the characters true colors shine. From D.Va having a skin where she dresses as a police girl, to one of her dressing as a catgirl, I think it is pretty safe to say that there are zero problems with her design.
Rating: 10/10
So, how hard is this character?
If you encounter a D.Va player that knows what they are doing, you'll run into some problems. Ironically, if both teams have D.Va, it feels a little unbalanced since there is literally two D.Va's facing off in an explosion (excuse my language) "pissing" match. You can easily be killed by her explosion, too. The best strategy is to run behind a wall when she activates her ultimate. You can easily tell when she does because she says "nerf this!" Sometimes the mech will be launched by her boosters when activating the ability, which leaves less time to run from her exploding mech. Reaper could easily dodge this by his teleportation. You could also look for D.Va while the explosion happens, because she doesn't go back into her mech until after the explosion.
Rating: 7.5/10
Well, that concludes my own character review for D.Va. Don't forget to upvote if you liked this. Comment down below for suggestions on the next character review I should do.
Final Score: 9/10(rounded up)
Sources:
https://overwatch.gamepedia.com/D.Va#Gallery
https://en.wikipedia.org/wiki/Charlet_Chung