In my opinion, adventure game is centered around a journey, or a narrative, and all of the other elements in an adventure games are in service of the narrative. This means, the more coherent and stronger the elements help in aiding the narrative, the better the game design. 

 

What the narrative of each game is another story. It can focus on exploration and immersive story-telling (like the way Skyrim handles the adventure part), to propose a philosophy or idea of the game designer (Stanley Parable, The Beginner’s Guide), or to invoke emotion from the players (Journey, Life is Strange). The narrative is core part of an adventure game, aka the make-or-break point of the game.