The lesson of Cars 2 can be summed up in "be nice to retards, they just might save the world."
Cars 2 opens fabulously, with a thrilling, action-packed five minutes centered around the British spy Finn McMissile. It is both legitimiate in its own creative right, while also being a spoof of spy films. This is the high point of the movie. It's all downhill from here.
We then cut to Mater, who is helping some car which has broken down in the desert. The dialog immediately shifts from witty and fun to being lifted straight from an episode of Full House. It. Is. Awful. It gets worse when Lightning McQueen shows up a minute or two later, since McQueen is not a moron, and any dialog between someone who is a moron and someone who isn't is necessarily going to be strained and unrealistic. And holy shit, is it strained and unrealistic. The relationship between Mater and McQueen would only make sense if written and staged like the relationship between Charlie and Ray in Rain Man.
Mater is a wholly unlikeable character for all but the youngest or stupidest. He is a raging idiot with essentially no redeeming qualities other than that he is not mean. This does not a person make. McQueen would not be his friend. Half of the shit that Mater pulls in Tokyo (spelled Towkyo... cute) would ruin a friendship in real life or in any other movie.
When McQueen feels bad for snapping at Mater, it should not be in the way of a friend as proposed in the movie, but in the way that one feels bad for slapping a dog for peeing in a corner. It makes no sense. And this doesn't even touch on the logical issues regarding McQueen's regret for not standing by his friend, when his friend happily abandons him during a race for a pretty lady. The lesson is hollow on all levels.
Mater takes up the vast majority of the movie, reminding you in nearly every second how contrived and stupid the setup is. His story is a fish-out-of-water tale where he is mistaken for a spy and it reminded me of The Man Who Knew Too Little. That was another movie where a goof is mistaken for a spy, but at least in that one, the protagonist is actually somewhat skilled, even if some of it is unintentional. And even there, it didn't work all of the time! So you can imagine how badly Cars 2 fails in this regard.
I liked Cars well enough. It was very simple, but pleasant. Cars 2, on the other hand, annoyed me at nearly every turn. It's fun for all the time that Mater isn't on screen, but he's on screen for 90% of the movie. Or if, barring reduced Mater time, they had toned down Mater's profound retardation by five to eight notches, it would have worked. But they did neither, and the movie suffers for it.