In my humble opinion, a vehicle's sun-visors are critical, and far too often overlooked. I'll use my '06 GMC Sierra as an example of how to do it right.
Now, many of you would absolutely hate the interior of my truck. From the giant grey plastic dashboard, to the intermittent rattle behind the instrument cluster, to the mouse-fur bench seat that cannot be adjusted for seat bottom height or angle, its a paragon of cheap. But the sun-visors are freaking fantastic!
Look at these felt(?) covered bad boys! They can be straight down for maximum shielding. They can flip all the way forward to be less intrusive. They even have bitchin' extenders for when the sun is in that awkward spot above the rear-view mirror. If I put the passenger side visor down, I can block off virtually the entire top of the windshield for the ultimate in morning eastbound or afternoon westbound commuting pleasure.
I can even swing them to the side, and block off the whole top of the side window. YEAH!
I'll contrast that, with the sun-visors from my wife's '06 Mazda 3. The Mazda's interior is far superior to my Sierra in every qualitative measurement ... except one. I'm pretty sure the sun-visors in that car were made by the Playskool corporation. They don't look bad, but feel like the same blow molded plastic a cheap drill case is made out of. Worst of all, no extenders! WTF?!?
What part of the interior do you think is the most underrated?