Feeling ill today so only managed a couple of brawl games but I finally got to try out D'va and my first thought was "wtf, why does she move so slowly when shooting? That makes no sense and should be changed". Also her damage is pathetic.
Dva can do quite good damage but she needs to be very close to her opponent. But if you boost up to someone and start raining bullets into their head for crits, they're not going to last very long, and Dva can chase for ages since her boost CD is so low. Dva also benefits a lot in those sorts of aggressive attacks by having no need whatsoever to reload. She has to be one of the best heroes in the game at taking out Mercy, since she can simply boost after her when Mercy flies off and finish the job.
Dva's biggest problem is that she goes down very hard to focused attacks since her critical hitbox is the size of the moon, so I hope that when they buff her, they tweak her survivability. I actually think her damage output is in a good spot; it's just that too many don't play her as the aggressive flanking tank she's meant to be, and really run right up to people's faces before shooting.