as a native German being married to an Iranian wife (that only came to Europe in her late twenties) and having travelled to Iran,
I can say that I have a quite different picture from the country than most people have when reading the media. So I come up
with a very random list of prejudices and what I found to be real.
1.) Iran is very strictly Islamic
I cannot speak for the poorer rural areas. But having a look at several Persian cities, I know that there are probably less strict muslims in private than there are strict Christians in the USA. The government is Islamic, sure. But regular people have a very relaxed view of the topic. I know many who are even aggressive atheists.
2.) Muslims don't drink alcohol
Maybe that is true for strict muslims. But for regular Iranians, the opposite is true. I almost never drink alcohol myself (less than my wife), but in Iran, they drink alcohol everywhere, so I drink daily. Alcohol is very expensive, but virtually everyone has his dealer.
3.) Women are weak in Iran
Women are getting stronger and they fight for their rights. They study all kinds of professions, especially professions that are typical "men" jobs in the western world. 50% of computer science or engineering students are female, a number unseen in the western world. While rare here, it is common for me to talk to Iranian women about stuff like agile software development, the latest database frameworks or the safety of car factories. My wife, as an example, is an industrial engineer.
In Iran, women still have to wear a headscarf, but only few wear the iconic black chador. Many are dressed very fashionable, while still obeying to the government rules. Women are also allowed to run businesses or drive cars and travel alone. Iran is not to be compared to Saudi Arabia.
4.) Iran only has oil.
While the build quality is not like in the west or far east, they produce millions of cars every year (sometimes they just assemble the parts from western, especially French, models). They are sold throughout the middle east. I've never sat in a car not produced there when I travelled to Iran.
5.) Iranians don't laugh
The clerical government seems not to be funny, but that is not the reality of ordinary people. Iranians are very funny people, they tell a lot of jokes, like funny things, talk a lot. There exists a number of good native Iranian TV/DVD shows that make you laugh even when you don't speak a word of Persian. And they dance a lot! While dancing publicly is forbidden in Iran, everyone I know does it in private with guests.
6.) Entering the country is dangerous
I found that at the passport control in the airport, the guards are usually very welcoming and very friendly. This is in stark contrast to how it is depicted in films. They usually want you to "come back soon" when you leave the country. The usual tourist will have a wonderful time in the country and probably make friends with a lot of very open people.
7.) Persian is difficult to learn
It is easier to learn than English because of its beautifully simple grammar that knows no exception from rules. No articles, no masculine/feminine forms (which makes it the perfect feminist language in theory). Learning to write Persian-Arabic script only takes you a day or two.
Go visit Iran while the Grand Bazaar of Teheran is still free from tourists!