For me personally, When you Believe is one of the greatest and best duets ever recorded..

but how do you feel about the legendary collaboration of the ultimate voices of all times?

A duet by the two best vocalists ever
So grateful that it happened, I'd give it between a B+ and A- because if the song was a Mariah written original, it would have slayed even more

A

It's flawless, I was just listening to it yesterday Definitely an A!

A+ . I liked the song much more after I'd listened to this live perfomance

This song contains the most flawless blend I've ever heard from two vocalists. So tight, so pure, so in tune (pitch-wise and with each other) you couldn't even tell who was who at some points.
However, Mariah once said the song would've been a lot better if she wrote it and I agree.