Visual aspects of an animated film can make up for other other shortcomings though, and add an extra layer you can enjoy. It's not the most important thing obviously, my favorite animated show is Home Movies after all, but it's clearly something you need to consider when you talk about the quality of an animated work.
I'd honestly argue "Let It Go" is better than a lot of Disney songs, and fairs well against the best Disney songs. Overplayed as hell, but it's a strong, emotional song.
It's true that the story in Frozen wasn't anything special, and the characters less so, but they weren't so bad that it became a worse film than any of the unneeded, poorly animated cash grabs Disney has done in the past. Not all the straight-to-DVD sequels were bad of course, of the ones I can think of, The Little Mermaid 3 was alright.