The distorted images in the side panels is called Edge Distortion. It is common in nearly all triscreen games. Some are less than others though.
I thought edge distortion just caused stretched characters. Does it cause objects to appear closer than they are as well?
There is a FOV setting in the Advance Settings in the HL-2 menus, somewhere.
I found the setting, however I can only adjust it from the default main menu screen, and toggling the setting only seems to affect the default menu screen. In-game doesn't seem to be affected either way. I'm not even sure which way I should set it, if I could.