I know a Brazilian at work and I am fluent in Spanish. When he talks I can't understand what he is talking about. I pick out words here and there (about 50%+) but that doesn't help in determining what he is talking about. Enough of the words don't sound the same that it's not really possible to communicate easily. I tried to help a Brazilian tourist once at Best Buy and HOLY CRAP I swore I understood the words but they apparently don't mean the same things
. Also I have no problems speaking and understanding Spaniards.
I guess a good example is that old Lambada song. I think I understand quite a few of those words, but I don't know what the song is trying to say. It's like if you make a song with just random words thrown in to make a sentence (at least to me)
That said, i'm sure it's easy to learn if you are fluent in one of them. I picked up French easily since sentence structure is very similar you just need to memorize words.
FYI I learned Cantonese first, then Spanish, then English was my third language. On top of that my wife is Czech so when we have a kid it's going to get interesting.