The 2000s were definitely Pixar's golden age. They made great films before then (e.g. Toy Story), and they've made great films since then (e.g. Inside Out), but the 2000s were an incredible run of very original stories executed impeccably.
Interestingly, of the Toy Story series, Toy Story 3[1] is considered by many to be the best of them (and one of the best Pixar movies overall as well). Sequels can be done well, even if they often aren't.
1: Just thinking about the ending now is making me tear up a little. I think the older you are, the more aspects of your life it will likely relate to.
