Heroes of the Storm is a MOBA game developed by Blizzard Entertainment modelled very closely on League of Legends. It features characters from Blizzard's Warcraft, Diablo and StarCraft franchises. Heroes of the Storm is currently only downloadable via the Battle.net Launcher.
The game is touted as a free-to-pay MOBA (Multi-player Online Battle Arena) with the player able to control a "Hero". Heroes are characters from the above-mentioned franchises, each of them possessing unique abilities. Some are available on a free-to-play basis (with heroes currently being rotated six-at-a-time), while some require purchase outright, either with real money, or with gold that is accumulated though playing the game. Different styles of mount, and skins for characters are also available, either unlocked at certain levels, or able to be purchased with real money.
You control a character ("Hero"), and each team requires five heroes. Maps are battled between two teams of five. The end goal is to destroy the enemy's fort, with maps offering differing ways to either directly assist with destruction of your enemy's structures, or debilitate the enemy units enough for you to do the heavy lifting.
The hero that you control 'levels up' during the course of the battle, acquiring abilities as s/he increases in level, with each offering allowing the player to pick one of several skills.
Another unit that appears prominently are Minions. Minions are always the first unit that an enemy turret starts attacking, and only after the supply of Minions for it to target has gone do they focus fire on you and other allied Heroes. Each map has three routes to take to each your enemy; North, South, and Middle. Each fort periodically sends out three waves of minions, one in each direction. Between the routes, there can be located both map-specific mechanics, or mercenary camps. Mercenary camps are groups of AI-controlled NPCs, more powerful than Minions, that will join your cause if defeated in combat. Most camps require more than one player to defeat.
The game currently supports three modes; Practice, Cooperative and Versus. Practice is where you control your character, backed up by 4 AI Heroes, with all 5 Heroes on the opposing side also controlled by the AI. Cooperative is where you (and friends, if so desired, but will search for random players who are looking for a group to fill gaps) can battle against an AI more appropriately matched to your skill level(s). Versus is where you and other human players (including friends) can battle against other human opponents. All three of these game modes are marked "Casual".
There are two game modes introduced to the menu system in the September 10, 2014 patch; Draft and Custom Game, both of which are marked as "Competitive", and neither of which are available at time of writing. The September 16, 2014 patch included a number of bug and stability fixes.
Heroes of the Storm also has a Store, accessible within the game. Here, mounts, skins and heroes can be purchased, for either gold, or real money.