Commercial viability.
When directing a game, ensuring the commercial viability of the project is a key role. This covers many areas, from ensuring it hits your target audience and is something they can relate to, meets their expectations in terms of quality and features, is accessible in terms of usability and challenge, has marketable hooks that will differentiate it, and how the game generates revenue.
There has never been a more interesting time in the games industry for how you bring your game to market and monetise it. Business models are increasingly influencing a games direction, whether that is digital delivery, free to play, episodic, user generated content, or games as a service. The method you are going to use to distribute your game, and how you intend to monetise it will have a direct influence on the games direction.
There needs to be a balance of commercial and creative objectives, and these really need to be agreed on with key stake holders early on. It needs to be a fundamental part of the vision, in the art, game, audio and technical direction. It's not only about making sure it appeals to a wide enough audience, but how you can monetise the experience and generate revenue.
In its simplest form it's about how you structure and distribute your game. Creating a box product is relatively straight forward, if youre planning a franchise then you will have sequels in mind and that will influence the narrative and future feature sets. A similar thing applies to digital distribution, the scope needs to be expandable in terms of features and content, the narrative needs to be able to naturally expand, downloadable content needs to seamlessly integrate.
Unless you're a developer who doesn't require income and sees game development as purely self-expression, then you need to have a commercial focus to your work. Your creating an experience that you hope will generate revenue, and whatever business model is chosen has to influence the direction of the project. It has to provide a suitable return on the investment and provide an attractive value proposition to the player, i.e. what they get for their money. You have to make sure the direction and team are aligned to these goals as well as the creative ones.