'Cars' is the worst-rated of all the Pixar films (around 75% on average from critics compared to the others which are mostly in the 90s.) I've never seen it personally so can't judge but the general consensus seems to be it's not as good as the other Pixar films.
I sallute you! I love Cars too, I think it's really underrated. Great story, characters, jokes, and visuals. Really glad they're making a sequel though have to admit I'm surprised since it was the least successful/rated.
Haven't seen "Up" yet, can't wait though!
In no particular order: Cars, WALL-E, Toy Story 2. Very sore to miss off Ratatouille and Toy Story 1 though. Love The Incredibles but don't think it's as good as the others. And don't get me started on Finding Nemo...