After studying Spanish on my own for a number of years and four semesters in college, I am able to understand a fair amount of Spanish spoken on documentaries. The Spanish speakers on the docs tended to speak at a reasonable pace and enunciate well.
However when trying to understand Mexican soap operas, I was/am almost completely lost. Los actores hablan demasiado rapido.
A friend from Columbia once told me that Mexicans speak a “hillbilly” form of Spanish (her words) that sounds awful to the rest of the people from South and Central America and to people from Spain. I can’t tell the difference, but she could easily pick out where spanish-speaking people were born or how they learned spanish as a second language.