Let me just say right now that I loved Toy Story 2 and 3. Somehow Pixar managed to improve on a masterpiece each time and managed to make films about toys which still make me sob (I can't help but cry every time Jessie sings 'When She Loved Me'). However those two films were rare jewels in Disney's line of sequels, which are often terrible successors to great films, and for some reason they seem persistent to continue this trend.
Following the Disney Renaissance, beginning with 'The Little Mermaid' in 1989 and ending with 'Tarzan' in 2000, I think it's fair to say Disney hit a bit of a creative block. Let's face it films like 'Home on the Range' were going to fail after 'Pocahontas' and 'Beauty and the Beast'. Disney then started churning out direct-to-video sequels of many of the classic films. I'm not saying all of these films are bad, but they don't stand up to their predecessors and the Disney legacy.
Unfortunately Pixar seems to be starting down a similar path. Later this year Monsters University will be released, whilst Finding Nemo 2 (rumoured for release in 2015) and Toy Story 4 are reportedly in development. This worries me. These films may be amazing and prove me wrong (I really hope they do) but it just seems Pixar are running out of ideas. The Toy Story sequels have admittedly become classics and I would love to see more from the characters in Finding Nemo, but don't belittle their legacies by rushing and producing less than stellar films. Make sure there's a valid plot and give the films enough time to be made properly and whatever you do never make a sequel to 'Wall.E' or 'Up'. Those films are perfect just as they are
That's my slight rant about Pixar and sequels over. Now for something a bit more positive but still related. Disney finally seems to be turning things back around. 'The Princess and the Frog' and 'Tangled' were both amazing film, which I hope will be regarded as classics in years to come, and 'Frozen' is sounding better and better the more I hear about it.