It IS very soon, however, we have not seen this kind of reception to a Disney animated film in over a decade, and certainly not during the era of social media. It was in theaters for over three months, which is practically unheard of in this day and age. "Let It Go" was number one on iTunes and Billboard. And, more importantly, it has inspired people. There is a TON of fan art, fanfiction, and more; youtube is flooded with various covers and remixes of the songs. I don't think Frozen would've caused that kind of reaction if it were just a flash in the pan.
I feel confident in saying that Frozen is at least the equal of the best of the Disney Renaissance era, such as Beauty & The Beast, Aladdin, or The Lion King.
And besides, the Cars franchise isn't considered Pixar's best, either, and people LOVE Radiator Springs over in DL.