I never play any games at easy either. Normal and then hard. One exception was Caesar 3. That game I played on very hard, and that is the only way to play it.
Steam is pretty user friendly. It has a lot of good features. That said, I will most likely get a boxed copy of hl2. Maybe use steam for other add ons.
I would think a lot of rockets (hmm....8 to 10?) should bring one down. If all you have is a machine gun, you will probably have to avoid it as best as you can.
I feel high brightness and contrast is a lot of strain on the eyes. I have brightness about 40% and contrast about 75%. A super high gamma setting makes me woozy.
The last time voice acting blew me away in a game was in Grim Fandango. But that was an adventure game. Never saw outstanding voice acting in an FPS before.