Huge news for Marvel really - they would basically get ALL the characters back in their stable - since they already made the deal with Sony for Spiderman. Could we get the impossible? A good Fantastic 4 movie?
Also sort of a big deal to Star Wars in that Fox still has video rights to Episode IV, so would allow Disney to distribute the movies together, but I can't say that is THAT big a deal.
20th Century Fox also distributed Avatar, so not sure how that would affect the future of Pandora.
Otherwise not sure that it would affect much in the parks...Universal would still have the theme park rights from Marvel in Florida, and Fox doesn't really have many other significant tent-poles that would make for good theme park material outside of Marvel. Alien - already did that. Predator? Die Hard? Their only kids properties are Dr. Doolittle and Ice Age - both "No thanks" in my book. I would assume since they aren't getting the Fox network it wouldn't bring in Family Guy, and Universal already has the Simpsons.
I think the biggest bit for this would be their plans for their own streaming service. If they have the whole Disney and Fox back-catalog looked up under their own service, that's a pretty big deal.