Okay, lemme get a few things out of the way because people seem to have trouble grasping these for some reason
1. Planes is being made by Disney...NOT Pixar. The closest thing Pixar has to a hand in it is that Lasseter is producing, but he produces a lot of non-pixar works these days, so it's whatever (and to those assuming it's going to be crap just because it is disney instead of Pixar, just remember that Disney did do wreck-it-ralph)
2. To all the people going "Disney is forcing them to make these sequels!" that's not exactly true either. While it MIGHT be the case for something like Monsters University or this film, it's not the case with Cars 2. Lasseter has said in several interviews that he really likes the Cars universe and he really wanted to do the sequel. So no, Disney didn't force anyone to make that sequel.
Okay, now on topic...I admit, I have very mixed feelings about this. I knew they were making a Finding Nemo sequel, and I was mostly okay with that idea, because I honestly look at Cars 2 and (what I've seen of) Monsters University.
'cause really...look at those two movies. They aren't so much sequels as they are movies just set in the same universe while sharing characters.
I look at Cars 2 and I see it as Pixar's attempt to do a Spy movie (and it wasn't a bad spy movie) first and as a Cars sequel secondly. It just seems like they wanted to do a Spy movie and then decided to have it in the Cars universe, and I personally think it worked pretty well (but I'm one of those weirdos that liked Cars 2 more than Cars 1)
Same with Monsters University. I see it as Pixar wanting to just do a college movie. Their own take on Animal House or Revenge of the Nerds or Van Wilder, just with their own Pixar take on it. Personally, if they wanna do a college movie, I'm actually kinda glad to see it in the Monsters, Inc. universe than if they just tried to do people or something.
And I think that's why I'm (currently) sort of on edge about Finding Dory. After Cars 2 and Monsters University, I figured Pixar used these sequels to mix things up some. To take an existing world, and not just do a sequel to it, but do a new kind of story with it. So I just assumed the sequel we were getting would be Nemo and Friends but on a new type of adventure.
I didn't think they'd be so quick to go back to having a character disappear under freak circumstances and have other characters face the ocean depths to go after them.
Now I'm willing to reserve final judgement until I see more, but from what we've heard, unlike Cars 2 or Monsters University, this seems like their sequel idea is to take the first one and give it a fresh coat of the same paint rather than trying to do something new or interesting with the world it takes place it.
I could go on and on about my thoughts on this matter, but I've said enough for now.
I have to say though, it's actually really nice to talk about this with people.