It is a very hard question to answer, the main difference is the pronunciation, also the tone of the voice. Another thing to take in to consideration is the use of words, for example here we say ''pavement'' in the USA they say ''sidewalk''
A Colombian friend of mine who is learning English has a CD that she listens to, on the CD they translate from Spanish to English, they read out the text first in British English and then in American English. If you could listen to a CD like that, you would notice a big difference between the two accents.