I think modern tints that don't discolor look good within reason. 5% and such is pretty ridiculous, but I think up to about 20% looks good. It does help a lot with cooling the interior as well.
Tint was one of the best things I did to my old Ranger. It had a dark gray vinyl interior that would get scorching hot in the summer. 35% on the sides and 20% on the back window helped immensely. That was the darkest I could legally go in NC. My current truck has factory tint on the Super Cab windows and rear window that is about 20%, and that is a must on a black vehicle in the South. I have considered getting tint on the front side windows too, but I don't think a light legal tint would help much on just those two windows.
I've got no problem with other people tinting their windows as dark as they want to, as long as they can clearly see out of the vehicle.