Blizzard's continued growth of champions in Heroes of the Storm puts the onus on them to make the heroes unique in more than just look. What would the purpose be of adding a new character if its just going to play the same as one already in the game? Well, the designers are doing a great job of keeping the game play for each new character unique and the upcoming addition of D.Va from Overwatch is no different. She has two modes, Mech and Pilot. And while Mech appears to be the more powerful and desired of the two modes, Pilot gives you a second step before being killed where you can change your situation and build back up to generate a new Mech. In Mech form, D.Va appears to be a bullying tank that can attack and move at the same time. But after taking a certain amount of damage, the switch to pilot mode becomes a powerful ranged attacker who can't fire on the move and who becomes a lot more vulnerable. It's like playing a Prot Warrior who becomes a Fire Mage every once in a while. It should take time, but I can see how both modes could be used to the players advantage if done right.
Here is more on D.Va's game play as Blizzard puts her in the spotlight.