Defence of the Ancients 2, don’t say we didn’t warn you.
The original Defense of the Ancients (DotA) was a mod of 2002 release Warcraft III that turned the real-time strategy game into a multiplayer online battle arena (MOBA) that pitted two teams of players against each other. This sequel has been in the works since 2009, but only recently released.
Combining aspects of a real-time strategy and role-playing games, it should not be a surprise to hear that it plays much like World of Warcraft. Presented from overhead, players pick a hero to play, and using melee and ranged attacks, attack enemy creeps (basic foot soldiers that spawn in perpetuity and are controlled by the game's AI) and heroes. Defeating enemies nets gold and experience, which can be used to upgrade the abilities and equipment of your hero.
A multiplayer game, Dota 2 has five players per team going at it on maps that have three paths connecting the two teams, with a river dividing things down the middle. The objective is to destroy the towers that line the enemy paths, penetrate the enemy stronghold, and destroy the enemy "ancient." Your game doesn't end if your hero dies. You lose a bit of gold, have to wait for regeneration, and then need to slog your way back to the front lines. It's just enough punishment to make sure you want to be careful in how you wield your hero.
Managing the many levels of complexity here takes some practice, and with dozens (hundreds?) of items to acquire, equip, and combine, Dota 2 isn't for the faint of heart. It's simple in principle, quite difficult in practice.
If you choose to play the game as it was intended, online with real-live teammates and opponents, you could also be opening yourself up to the kind of bad and offensive behaviour that has become the stereotype (which is fine if you like that sort of thing). But Dota 2 is free to play, so it costs you nothing to give it a try.