I look at HotS as a pretty solid game, but it's what they aren't doing with it that has me perplexed. As a singular platform for their entire game portfolio, it has SO MUCH untapped potential. Blizzard's team have amassed a vast asset library from EVERY IP under their umbrella. Some of the most impressive character models... and a ton of voice acted lines... and great audio...
Why not either...
A) Start delivering PVE campaign packs.
They could be structured similarly to Hearthstone adventures. Every once and and a while, put a PVE adventure up on the store for $X. Cool PVE content with some lore nuggets for the respective universes.
Here's just a quick example. They put a Warcraft adventure called "Ravencrest's Legacy" involving Illidan's origin story. When this happens, maybe it adds a new map to the rotation of the base game (Black Rook Hold) for everyone for free as part of the launch event. But if you buy the adventure you get a PVE campaign with a small storyline involving Illidan during his beginnings as a hero against the Legion with the Ravencrest family. As part of the package, you get a hero, and like 2-4 thematically related skins for other heroes.
Let's say as an added bonus, (given it's an Illidan storyline) if you complete the adventure you get an Illidan in mage garments skin, what he looked like as a magic wielder prior to consuming fel magics.