half life 2 should work without any problems. even if in crossover. although what you might want to do is set some 'advanced' options before starting the game. you can find these on the net. they can essentially disable sound, or certain graphics things so that you are able to narrow down the problem. you might also want to see if the game works if you boot into windows through bootcamp and then run steam that way. if it works then turn down all the graphics options and then try again in mac.
otherwise you could just contact steam, they are normally helpful