I'm a little hesitant on this one. Something tells me this film may only be made solely for merchandising purposes. On the other hand, Pixar proved they can indeed do sequels well (Toy Story, anyone?).
Don't get me wrong, I have the utmost confidence in Pixar, since TS3 was a huge and I mean HUGE cash-cow, and it's one of the best animated films to hit the silver screen, grossing over a billion, critics worshiping the ground it walked upon, etc. I think they're going to blow us away once again, even if the first Cars was a bit of a let-down (It's great, but doesn't hold up against other Pixar films)
These two mouthfuls aside, we can't really say anything until it comes out. Only time will tell if this'll be another shining trophy for them or if this'll be their first clunker. All we can do now is speculate.