Gaming is an innovative industry by nature, with every game the way we make games improves along with the quality of the games themselves; but through this innovation we also push boundaries and push into new genres, and when these new games are hard to define, we often lump them in as 'Action-Adventure game.'
Wikipedia defines action-adventure games as, you guessed it, a game with the qualities of an action game as well as an adventure. It defines an action game as a game that requires quick thinking, skill, and reflexes; while adventure titles feature puzzle and role-playing elements that need more careful planning as well as a story centric gameplay. Now that seems fair as a definition until you realize that every game on the market features opportunities for planning and story as well as fast paced combat encounters. The action-adventure genre literally covers every game out there (with the exception of a few purist adventure indie games.)
The main difference between adventure games and easier to define RPGs is adventure games don't give the player as much choice. Adventure games might feature open worlds, branching paths, etc., but every playthrough is more or less the same, where as an RPG features varying storylines and encounters based on your choices.
Lets look at the 'quintessential' action-adventure "The Legend of Zelda" for any gamer who lives under a rock and has not yet played this series, go play it; for the rest of us, lets continue. Zelda games feature exploration in an open world, it includes many puzzles and long term 'quests'. However, it also features fast paced hack and slash combat and intense boss battles. Zelda is not an RPG as I hinted at yesterday, player choice has little to no effect on the core storyline, but we cannot keep calling it action-adventure either. Other games that are given the moniker include Assassins Creed, Red Dead Redemption, Grand Theft Auto, Infamous, yeah, games like that. All feature open worlds with intractable 'flash points' to start quests and gain objectives, they are all adventure games as you follow a single character through a story based adventure.
So how do we define these games, I say adventure-sandbox. They aren't pure sandbox games like Minecraft, they have objectives; however they all put emphasis on exploration and interaction in an open world much like a sandbox game, but this isn't is for action adventures.
Tomorrow I'll talk about sub genres within my new 'adventure-sandbox' genre specifically with the example Assassins Creed vs Red Dead Redemption