Maybe it's offtopic but my guess about Half-Life 2 is that it's base
graphics engine Source for now only has Direct3D support, not OpenGL.
However, I hope they will port also this game to OS X, so they will
create OpenGL support and from there it is rather easy to port this
game to Linux.
And I don't think that Valve would be against Linux port - of coarse,
they won't this because it could be done by other companies - but we
still have to wait for such things to happen.
But for now, AFAIKAS (Know and Saw) Half-Life 2 runs under Cedega
(that TransGaming thingy) officially - as one colegue rushed trough
demo using Cedega and our Debian-based tweaked distro.
but: less linux gamers, less games ported to linux
:'(
there is the ut series, and all stuff from id. but no halflife 2
-tom