I've recently started plowing through HL2 and the episodic content (currently starting out on Ep 2), and have noticed a weird problem.
It seems that after an undetermined amount of time, my computer will crash. My computer is a notebook with an Nvidia dedicated graphics chip...its good enough to run HL2 and Fallout 3 (but as I'm away from it now, I don't have the specs handy).
I can combat this crashing issue by periodically alt+tabbing to my desktop and letting my computer relax for a bit.
On another note, my fans are completely clear when I play...airflow should not be a problem IMO.
On another another note, I have absolutely zero problems playing TF2 or CSS....TF2 will lag for me slightly if there is too much going on at once (i.e. 32 player mayhem), but no crashing.
My graphics card is an Nvidia GeForce 8600M GT