Highways feel post-apocalyptic to you?
There was only two raider groups (unless you count the Great Khans), were hardly any ghouls or irradiated mutations (You can really play the entire game only running into Giant Geckos, I did on one quick playthrough)
It is not really post-apocalyptic, just the setting, not the feel or anything.
There were few raiders cause the lands were more civilized by NCR and House but there are still signs of a fictional universe taking place in the post-apocalypse, for instance, people walk around with guns in the street.
Ghouls aren't some kind of epidemic, they're not really suppose to swarm over the area.
Look at FO1, only ghouls were some in Hub (IIRC) and Necropolis.
Look at FO2, there were some ghouls in Broken Hills and Gecko but other than that there weren't that many others.
Irradiated mutations?
Anyway, I look at the game and what do I see?
I wake up in Goodsprings and see Bighorners the size of elephants.
I go on a quest to hunt penguin lizards.
I go to sloan and find a giant molerat.
I go further down to Primm and find a town taken over by a bunch of escaped convicts, with the local military just outside not being able to do anything because it's a low priority target.
I go further down south and find giant ants the size of bears.
I go east and find a town burning to the ground with people crucified and find a bunch of men in roman esque clothing with their leader who's named Vulpes Inculta wearing a wold-head-hat.
Maybe I don't see radiation every 15 feet, maybe I don't see raiders every 15 feet, maybe I don't see a crater every 15 feet, but I see enough to admit that this isn't normal, this isn't like the real world at all, something has happened to make these areas, creatures and people like this, something big, The Great War.
The Great War happened, out of the ashes these things were born.
Again, it doesn't have to look like it was bombed yesterday for it to feel like the post-apocalypse.
Just look around at the people of the wastes, look at the laws, look at the wild life, look at the various factions.
I can't look at these things and say that it "doesn't" feel like the post apocalypse. (Or maybe post post apocalypse.)