Just got back from seeing the film, and I loved it. Doc Hollywood all the way, but the car concept is executed so well that the plot still feels ultimately fresh and of its own weight. Movies are most successful when you get lost and absorbed into them -- and it's even more incredible when the movies just happen to be animation. More than once did I have stirrings of "roadtrip!" as I was watching, and my own passion for driving cross-country to California suddenly began to resonate.
The film was lengthier than expected, but was satisfying through and through. The animation and scenic backgrounds are a joy to watch, and the accompanying sound roars along like a well-tuned Mustang. The accuracy of the vehicles featured was a cool touch as well; I noticed a Mazda Miata, the Ford Winstar, and of course, the Porsche 911. Many, many people seem to disagree, even calling it the film's lowest point, but far and away my most favorite scene was Sally's flashback exposition of Route 66 and Radiator Springs. It gave the film that much-needed emotional push, and served as the fundamental underpinning for the story's resolution. Tractor-tipping comes in a close second. ;)
I'm fitting Cars in at number four as my favorite Pixar feature-length animation, just before The Incredibles and just after the second Toy Story. I think what I liked most about Cars is the fact that there are no 'people' involved whatsoever. The film is so self-contained in its own world that it was just so easy to get into it, and live in its fantasy.
Like so, then:
1) Monsters, Inc.
2) Toy Story
3) Toy Story 2
4) Cars
5) The Incredibles
6) Finding Nemo
7) A Bug's Life