Before I came here, I did a bit of digging about on the internet, trying to find out about the Corsican language. There wasn't hellish much info in English, and even in French it was pretty sketchy. Now I'm here, though, and I've picked up a book of Corsican grammar (in Corsican, just for the hell of it) so I can start to puzzle it out for myself.
My first reaction from some of the free resources online was to describe Corsican as "Italian with a Catalan accent", because of the vowel reduction in unstressed syllables. However, vowel reduction in Corsican is not as extreme as that in Catalan.
One thing that wasn't described too well in the sources I'd viewed online was consonant changes, and in reality it isn't particularly difficult. I'd been trying to puzzle through single and double consonants, and my initial reaction was to treat them as in Italian, where a double consonant is lengthened (a process called "gemination". But the first pronunciation guides talked about consonant changes -- a T being pronounced as D for example.
As it turns out, in the south the model is more like Italian -- T is /t/ and TT is /tt/ -- and in the north these changes occur, but even these aren't alien to someone familiar with other Romance languages. It's a process called "lenition" (the weakening of consonants) and it happens frequently in many peninsular Spanish dialects (the archetypical example being the word "Madrid" in a Madrid accent) as well as in almost all other dialects in the letter V. A consonant is weakened with it occurs "intervocalically" (ie between two vowels). The strong form occurs when bounded on one side by another consonant. And if there's no other consonant, just doubling the same consonant gets round the problem (which is roughly analogous with the R/RR distinction in Spanish and several other languages).
So in the north of Corsica "atta" would be pronounced /'ata/, "ata" would be pronounced /'ada/ (as would "adda") and "ada" would be pronounced /'aða/ -- which is the same soft D as in Madrid (/ma'drið/).
So Corsican is just another point on the spectrum of Romance languages. The interesting part is how the north and south have such different ways of rendering the same consonants, but that in so many respects the northern and southern dialects are extremely similar and consistent. Before starting on Corsican, I would have assumed that such a large difference in pronunciation would have broken mutual comprehensibility and that the dialects would have diverged to the point of being considered completely distinct languages, but that doesn't seem to have happened.