As console hardware improves with each passing year, more and more are video game studios and developers making immersion the primary focus of their titles. Priorities change with each fantasy being depicted, but there are a few constants that most adhere to; graphical detail, customisation and a seamless UI. All help sell the idea that the player is living the world they've created, but each game is always going to have something else to help sell that idea even further.
Say you're playing an iconic superhero who has the ability to fly. Developers are going to make nailing flight and traversal their first concern, as, if they get it wrong, the entire house of cards could come tumbling down.
Yes it should go without saying that an FPS needs to nail shooting mechanics or that a racing game needs to make driving feel authentic, but there are nuances too; elements of the experience that form a part of a unique mechanic integral to a given title's success.
Sadly, even the greatest games don't always manage to get everything right - either out of ratings restrictions or even just the limitations of certain hardware. They're by no means make or break, but they're significant enough that they can end up taking you out of the experience altogether, and no one wants that.