Marvel Heroes is a persistent universe role-playing game set in the Marvel superhero universe. Dr. Doom, the main opponent of the Fantastic Four, gained possession of the powerful Cosmic Cube which he plans to use to gain control over the world. The player takes the role of a superhero, e.g. Captain America or Deadpool, in an effort to stop Doom's plan. But unfortunately he is also aligned with many of Marvel's iconic supervillains which need to be disposed of first...
The combat system is reminiscent of Diablo II: the player character is controlled indirectly and attacks by clicking a lot on enemies. Each character has a standard (either melee or ranged) attack plus a few special attacks which drain spirit (basically mana) when used. Otherwise it is the usual mix of fighting enemies, receiving loot and either equipping it for better statistics or selling it to vendors (alternatively it can be donated to slightly improve the vendors' supply). Solving quests and fighting enemies give experience points and eventually lead to level ups - then the character's statistics improve automatically and the player can invest a point into one of the three skill trees. There is also crafting which can be used to improve equipment with found ingredients.
In contrast to the hub areas with quest givers and periodically respawning enemies, the quest zones are all instances. The game uses a autojoin feature: when such a zone is entered, the player is automatically grouped with four other players who happen to visit the same instance. This can be deactivated, though. Regarding end-game content, players can participate in player vs. player matches (two teams of five each have to destroy the enemy's base) and a number of daily missions and group challenges (either an instanced dungeon or surviving enemy waves).
Marvel Heroes is free-to-play and supports itself with an in-game shop. Here players can unlock new heroes (currently there are 59 to choose from), costumes or other items for real money. New heroes can be also be purchased for Eternity Shards, a sort of currency dropping when defeating boss enemies.