Brightness and Contrast leave little to no room and are turned almost all the way up with the white scenes becoming gray vs white. Black is OK but murky black rahter than detailed black.
You could have the contrast or brightness turned up too much on the TV... many TVs come with these settings too high... perhaps your friend with the good looking cable HD has his TV adjusted for a better appearance.
I'm starting to think this is the issue. Turning the "sharpness" up on an HDTV actually tends to cause more artifacting than eliminating it like you think it would. Mine is almost all the way down.
mstar - try and find a Blu-ray or DVD with a THX optimizer feature on it and follow the instructions. This will help you properly calibrate your TV settings to see if that's the issue.