I loved the first one (in fact, I watched it again recently), and I especially liked how it's greatly enjoyable by kids and adults alike (The fact that the there was a character based on an Italian Fiat 500 made me even more interested to watch it as a kid, as my grandfather is a big fan of vintage cars, and was planning on buying one). The whole story and characters were great, and I'm happy I had the chance to watch it as a kid.
I saw the second one only once, at the movie theater, so I don't exactly remember every bit of it, but I remember enjoying the fact that it was something completely different from the first one. At that time at school we used to collect cards from different Pixar movies that came as a promotion with purchases at the local supermarket, and Cars was one of those. That card album made me even more interested in the film.
I saw this trailer recently, and honestly I'm as happy as I was as a kid when the first one came out, and I'm interested in seeing this new story (which seems very "Rocky" inspired to me, from the looks of it).