In my experience, many Spanish students are surprised at how hard they have to work to make substantial progress in the language. I think they initially assume that Spanish is easy to learn because its spelling is more or less phonetic, and its pronunciation relatively easy (except for the rolled r). This certainly gives the Spanish student an advantage at first over someone studying, say, French. But as one’s studies progress, the complexities of Spanish verbs and pronouns can be a rude awakening.
If it’s any comfort, there’s no question that other languages are even harder! According to the Department of Defense, Spanish and the other Romance languages are all Category 1 languages on a scale of difficulty from 1 to 4. (Category 4 languages, as you’re surely wondering, are Arabic, Chinese, Japanese, Korean, and Pashto.)
This means that if you undertake intensive language study at the DOD’s Defense Language Institute in Monterey, CA, it will take you only 26 weeks to achieve proficiency in Spanish, versus 64 weeks for a Category 4 language. (Going by this metric, Arabic is 2 1/2 times harder than Spanish!) Your classes will also have a higher faculty:student ratio, and you won’t have to score as high on the Institute’s language aptitude test to be admitted.
The Economist had an amusing article about less-studied languages that are also difficult for English speakers. For example, Botswana’s !Xóõ, has both tones (as in Chinese) and clicks. It’s so hard to pronounce that even native speakers develop lumps on their larynges.
Looking closer at the DOD language scale, It’s interesting, though not surprising, that a language can be hard for adult English speakers even though it’s easy for babies. Take Turkish and German. Turkish is famously easy to learn as a first language: babies master most of the grammar by age two. This is because Turkish grammar is remarkably clear–its many word endings are regular, distinctive (not homophones), and discrete, with each ending representing a separate bit of meaning (e.g., plural or past tense, but not both). In contrast, German is a challenging first language, with some aspects still causing problems in kindergarten because the grammar is so opaque. But because German is closer to English than Turkish, it is classified as Category 2 (35 weeks to proficiency), and Turkish as Category 3 (48 weeks).
For a point of view counter to the DOD’s, see Benny Lewis’s post on “Why Turkish isn’t as hard as you think!”.