Sequels have been getting a really bad rap lately, especially around Disney.
The most common complaint I've noticed is that they're "unnecessary", but really, just about every sequel is unnecessary. Star Wars (the first one) was a complete movie, and Empire Strikes Back wasn't needed. Harry Potter and the Philosopher's Stone was a complete movie/book. Godfather was complete after one movie. Back to the Future was complete after one movie. I don't think there's any real difference in sequel-quality between a good movie that earns a sequel by being awesome, and an incomplete movie that demands one upfront.
In regards to Disney, people tend to point to two studios, Pixar and Disneytoon.
Disneytoon was a studio tasked by Eisner to generate huge profits by milking any IP that had any value in it, and they worked under terrible conditions, forced to make movies with shoestring budgets with no time to work. The people who made Pocahontas 2 weren't even allowed to watch the original movie before making a sequel to it (Disney was lucky that some of them had seen the original movie in the theaters when it came out, and sort of got the gist of what movie they were supposed to be making). After Lasseter came in and fired the studio head, Disneytoon knocked it out of the park four times in a row, with Tinkerbell 1-4. I won't defend Tinkerbell #5, but it's no worse than Disneytoon's previous output, so they've obviously still got some junk in their system, but four good movies in a row is shockingly good for this studio, and IMO, it clearly draws a line between the Eisner era's approach to crappy DTV sequels and modern day Disney.
Pixar didn't have the sequel rights to their movies until they merged with Disney, and now that they have them, they're making the movies that they want to make, which includes sequels. Unfortunately, their sequels don't have a very good track record, but I think this has more to do with the studio, and not the concept of sequels by themselves. Pixar is seemingly in a slump, and they're putting out movies that they think are good, but the audience doesn't agree. It might also have something to do with the audience expecting a constant stream of unique innovation from Pixar, based on their pre-Disney lack of sequels, and the wide variety of their movies. This is an issue that Pixar needs to figure out, not some sort of mystical curse placed on Disney sequels.
IMO, one of the strongest things Frozen had going for it was that it was essentially another Tangled. It's already a sequel! I wouldn't mind seeing more from the other castles shown on the world map in Tangled, but Frozen 2 is fine by me, so long as WDAS can find a good movie in that idea.
