When people lazily throw out the word "overrated" when speaking about Adele, the easiest way I find to help them see that this isn't quite fair is to show them someone else singing her material. After all, if she was overrated, surely anyone could do what she does.
It's of course one thing showing them an amateur attempt to cover the British belle. But to watch someone as crazy talented as Celin Dion give one of her songs a bash, and still fail to recreate the magic, is way more demonstrative.
In fairness to Celine, though, this was just a little bit of fun- a professional like her fluffing the words it proof of that- but it's still an apt example of Adele being more than just a singer hitting notes. She brings an emotional weight and evocative delivery to her songs that isn't so easy to capture or recreate. And it's this ethereal quality that is connecting with the music buying public.
That, and a little bit of bandwagonism.....