Even the new Linux sound API, ALSA does not support 3D sound. Worse, game developers are confronted with a tangled mess of APIs, libraries, and hacks. X for Windowing, Mesa for 3D ALSA for Sound. And in addition make sure the whole thing works correctly with GLX as not to make the X server mad. All I have mentioned above would be fine, Linux IS still a growing operating system, if it were not for the fact that none of the above have remedies in planning.
Berlin is supposed to replace X, but still carries the baggage of client-server computing.
No new sound APIs are on the horizon, and no overhaul of the kernel to improve performance is in planning. At a deeper level, Linux is an operating system for programmers. Not only because it is difficult to use, but many of the paradigms focus on ease of coding, and compatibility with the Unix way, rather than performance and ease of use. Getting access to hardware required the program to go through layer after layer of abstraction, which effectively kills performance. Programs dump core files all over the place when they crash, taking up disk space if you aren't careful.