The big difference between ES and PT is the accent/pronunciation of letters and matching words. Secondarily, is the differing vocabulary. But a lot of these are still understood as archaic/uncommon alternative words.

(see shoen's post below.)

So, if you learn the accent of the other language, all of a sudden a large portion of the language is unlocked. This happened to me, almost like a light switch.

I don't have a lot of experience with Italian but it seems like the pronunciation is closer to Spanish.