Not an expert myself but i've got a decent amount of experience. I also currently live in a place with 12" concrete exterior walls...
Cons for concrete walls; they take up more space than standard construction thus increasing your footprint for the same living space, thermal mass works both ways, noise reverberates well like gunshots or the tv set real low two rooms away, r factor sucks, bullets bounce and skip off of them so a safe direction is questionable at all times.
Pros of concrete walls; bullets bounce and skip off of them, thermal mass, they reflect sound real well (we live next to a train track)
The R factor of concrete is 1.35 per 8" thick wall. Which is roughly a 1/2" peice of fiberglass batting or 2 sheets of 5/8 sheetrock (the same as a standard interior wall). Modern construction of houses provides r-13 as standard for an exterior 2x4 wall.
This place sucks in the winter the summer isn't bad since the south exposure is limited.