Battlegrounds maps “challenge the genre”.
Dustin Browder, game director of Heroes of the Storm, detailed the game’s Battleground maps at BlizzCon 2013.
“It’s not enough to pay homage to the games. We have to provide you with new challenges, and challenge the genre.”
More specifically, in the Blackheart’s Bay map you can deliver treasure to a pirate, who, in turn, will help you by turning the cannons of his pirate ship towards your enemies. In another area of the map, collecting and combining skulls with necromantic magic will allow the summoning of a colossal creature that fights to your aid.
In the Dragon Shire map, you can use the Obelisk of the Sun and the Obelisk of the Moon to access the Dragon Altar and summon a powerful knight to fight with you. Sounds nasty.