Architecture
The beauty of Iranian architecture apart, there are some mind-blowing facts about them. Just imagine, 2500 years ago they used the golden number to build Perspolis!
Four hundred years ago, Iranians built a mosque with acoustics by using math and called it Shah (Emam) mosque. There is a small square directly under the pinnacle of the dome. When you stand on this square and talk, it will echo your words several times. If you step more than 30 centimetres off the square there is no more echo.
The dome of Soltaniye is the tallest brick dome and the first double-wall dome of the world, built between 1302 and 1312 AD. The skylights of the dome act as a sundial. If the light comes through the hole in the main dome, it is noon. The light coming through big windows shows the time of the day in hours while the light coming through small windows shows the time in minutes!
Do you see this beautiful garden?
It is actually built in the middle of desert!
The Shustar Hydraulic System was the largest industrial complex before the industrial revolution. It's construction begun during achaemenid era though it was mostly built during the Sasanid dynasty. The main task of this structure is to block the Gargar river as a dam so that the surface of the water can be used to drain the tunnels in the slate. Gargar tunnels, however, provide water for residents of the area through the transfer of water from their passageways. Also by installation of open windows and ceilings, the miller could watch the milling wheels and water flow during the rest.
I could go on but let's keep it short. Anyhow, with or without any mindblowing facts, Iranian architecture is definately not overrated.
Food
Though the Iranian food served in restaurants usually aren't as delicious as what we eat in our houses as the real Iranian food, the food here is anything but overrated.
The natural beauty
I have already talked about Iran's natural beauty in another answer. Not only Iran's diverse natural beauty isn't overrated, but also is underrated.