I think that what appeals most folks to the Shrek franchise is its parodying of Disney films (this is also from the Disney execs POV as well) What people dont see until you actually see the film (especially Shrek 2) is how much heart the film is able to have and still be comedy with a deep theme (the inner beauty deal) behind it all. Which is why I was so glad to see this film in theaters.
Of course the previews tell you something different

And the insane advertising of the film was like Disney back in its golden age
Anywhos I was upset about Finding Nemo ousting Lion King (2D screwed from then on) But it didnt upset (more like surprised) me when Shrek 2 now claimed the new spot. For one thing, it had a good summer spot and sequels have a tendency to attract (especially those loyal to the original: makes me wonder if Spiderman 2 will oust the already succesful Spiderman 1)
I dont think the Incredibles will oust it but I think it will do well perhaps (between $100-200 mill)
enough of that though - oh yeah my last comment: I think the Shrek franchise should end here. Jeffery Katzenberg is becoming the Michel Eisner of Dreamworks by juicing this for all its worth!