The theme of the game is a group of heroes that are fighting a villain. The great part is there are tons of combinations you can try from different villains to hero teams and even different environments, and then advanced mode challenges once you start getting good at it. The expansions add even more of each type to play around with.
Each hero is typically played by one player and represented with a deck of cards that each have a different mechanics to represent their theme. The nice part is that each hero is complex enough so each player can has decisions to make on their turn, and it doesn't devolve into one person playing the game for the entire group.