The execrable state of input devices. I minimize the role of computer people in this, because they're so stiflingly inbred, so caught up in their own world that they can't see the real world. Not much potential for significant change in the game design industry. Games have settled down to their steady state in much the same way that comics have settled down. The comics today are, from a marketing point of view, not much different from the comics 40 years ago.
Computer games are now in the same position.
I very much doubt that games will ever evolve into anything like books or movies. The games industry had the opportunity to do so in the mid to late 80s, and it consciously rejected that opportunity in favor of short-term success. It has now worked itself into a small but profitable hole from which it can never extricate itself. Its audience is precisely defined, both in the positive sense AND the negative sense. Worse, everybody else knows it, too.