I think if used properly in some areas (maybe all, it depends i guess on the level) it would make it very pretty, at least more than it already is.
I know the HDR threads have been done to death i just had to share it with you guys.
Also read the "Beginners to Source" article on hlfallout, it talks about HDR and also the link to the program.
I guess they may not be putting to high a priority on it just because only high end cards can do it well, which also makes up a small percentage of people playing the game, at least according to their hardware survey.
What do you guys think?
NOTE: You will need a dx9.0 card and PS 2.0 to run this!