An Art Director is effectively the Captain of the ship; they are responsible for absolutely everything that goes into a game on a visual level. This includes: visual tone, quality, the art style of the game, what direction the visuals of the game goes in and the level of detail. Even the mood and colour is down to the Art Director.
This really is no easy job, the sheer amount of responsibility riding on his/her shoulders is tremendous, they practically own the game.
They're indirectly responsible for every object, texture, level, character and effect used in game and must consider it's every possible application i.e. position and use. Even studies such as composition should be taken into account, balancing the area as much as possible. Baring in mind there are often no fixed cameras and, given the opportunity, players will go wherever they want if allowed which means possible excavation of unsightly areas.
Another role of there's which I found quite interesting is the adherence to verisimilitude. How right something feels, as your immersion might slightly knocked off-balance if you saw Master Chief going around with a bloodied meat cleaver or a jungle with no vines and rocks, only trees. They have to make sure everything 'fits' appropriately.
The problem I find with Art Direction is that it doesn't seem as creative as, say, being just an artist. As instead of doing the painting and modelling, you're watching others do it, making sure they're doing it properly.
Like a farmer watching his pigs, he's just there to make sure they do what they do... whatever it is that pigs do.
Art direction for games is not too dissimilar from that of film making. You're required to consider every possible angle, taking into account composition, the 'weight' of the scene, lighting, colour and of course, story telling.
I feel (an uneducated statement right here) that film direction is far easier than game direction due solely to the fact that films decide where and what the audience sees whereas with games, mostly, the player is often allowed a certain amount of freedom to look around at the area, so vital components such as composition and lighting could be skipped over.
My ultimate career goal is to become an Art Director for a games company. Having now read up on what the role en tales, I can see where I need to improve; and there's a lot of room for improvement. First of all I'd need to become more fluent with communicating with others in a professional way, i.e. not sugaring the pill when it comes to criticism. On top of that I'd need to broaden my knowledge base of pretty much everything, as you never know what ideas might spring from. The fundamentals need a good fine-tuning such as composition, colour, mood, levels of detail and remaining consistent.
Definitely a lot of work to do before I'll become an Art Director although having seen that this job is less about the drawing/painting side of things and more about management, I think being an artist in the industry would suit me better.