This notion of 'difficulty' irritates me. GAME OVER IS ARCHAIC. DYING IS IMMERSION-BREAKING. The notion of a dead-end loss, or that by failing to do a specific task you are forced to go back and do it again until you get it right, is one of the major hurdles we need to jump. When a hero is beat by a group of random thugs in, for example, a comic, does he die? No. He is taken prisoner, he escapes, he whips out some new secret, etc. The idea that an artistic experience can ONLY be experienced by those who are skillful within the confines of its own esoteric community is pretty self-defeating. Literature is often panned, and rightly so, when it is written in such a way that it's only accessible or appealing to other writers. That said, when a book is accessible to the mainstream, but offers deeper philosophical insights to those trained to spot them, it takes a step in the right direction. Imagine if a book were written in english up until chapter 3, and then suddenly became klingon; anybody who doesn't speak klingon doesn't get to keep reading. Defending this piece as art would prove rather difficult.
Why then, have games refused to embrace more creative approaches? Laziness, mostly. Don't get me wrong, developers work hard, but I think a great deal of modern game design focuses on building an engine and designing the world and experience around that, rather than the other way around. You die if the goons kill you because the developers were too lazy -- or challenged for space, budget, or time -- to produce an alternative.
Which brings me to my next point, in that the video game INDUSTRY itself is an extremely crippling enemy to the medium. Think of the greatest literary works of all time. Do you think Dostoyevsky would have been able to effectively portray the angst of a dualistic class society in Notes From the Underground if he had a publisher breathing down his neck and asking for rough play-tests and bullet-point feature lists the whole time? Of course not.
This carries to film as well; to say nothing of commercial popularity, the most artistically and culturally relevant films have generally been produced by new or outcast directors or indie studios, been widely panned by their peers at the time, and achieved little success at the box office. They go on to find cult followings years later, as in the case of Fight Club, or are later recognized as having been ahead of their time, as in Citizen Kane.
From that, too, I think there is something to Ebert's argument that most games lack a singular vision, ie, a director. The specific pieces we gamers call masterpieces almost always have a master's name attached to them: Kojima, Miyamoto, Wright, etc. Some counter that even artistic films are produced by teams numbering in the hundreds, and this is true, but they all begin and hedge back to the root idea of a single person, be he a writer seeking to create a film that showcases the themes of human nature, or a director looking to do a new take on a specific genre.
By contrast, videogames are decided by the market. "First-person shooters are popular. Let's get on that. Kids like Space Marines, right?"
Yes, gaming can be, and will eventually become, an art form. But only when it is crafted lovingly by artists, and not chained down by an industry concerned primarily with money.
Of course, I am speaking in broad terms of gaming as a median and a whole. There have of course been flashes of brilliance. Hearing the music swell as I seize hold of a Colossus and the camera shoots outward to a dramatic pan. Seeing a secondary camera view of a police officer walking towards the bathroom as I stumble to clean up a body. Pathetically crawling away from a mushroom cloud and dying in the dirt.
Books may grip you from start to finish. Many films have been praised as having not one scene of excess; every frame is relevant and beautiful. Cite me ONE example in which the above moments of brilliance are extended into an entire game without lapse, and I will show you the poster-child for gaming as its own medium of noteworthy artistic expression.