Quick Summary:

The difficulty of a new language for you as a learner is partly informed by the languages you already speak. In particular, cognates will jump-start your vocabulary. For example, as much as 60% of French words are similar to English. As a speaker of English, you will not find many such cognates in Persian. This means you will have to learn more vocabulary. And then of course there is the Arabic script. It's not as hard to learn as you might think, but it doesn't make Persian easier for you (unless you want to skip it).

But that is where the bad news ends. The pronuncation is very regular - Persian is spoken the way it is written (very much in contrast to the worst offender in this regard, the English language). The Persian grammar is extremely simple and regular. There are no genders (no le, la, der, das). There are essentially no irregular verbs - once you know how to conjugate one, you can conjugate them all. There aren't any grammatical cases either, and the same plural suffix can be used with every word. That is a whole world of sweat and tears you can leave to those unfortunates trying to learn German.

While history has not recorded what Mark Twain thought about Persian, we do have a couple of choices quotes from other notable persons.