Christina : IDK, I got into her Music this Year

My Brazilian Fave : She doesn't Know what is a Chart, and She doesn't know how to Spell Flop, so, i really don't Know :-/

Who?

"E=MC2" wasn't a flop. It gave Mariah her record-breaking 18th #1 single, and has gone on to sell over 2.5 million copies worldwide despite the crumbling music market.
"Charmbracelet" and "Memoirs" are the ones that can be considered real flops. "Glitter" did not meet the high expectations on it but still sold over 2 million copies worldwide.
Madonna's "Celebration" is only a compilation album which has already sold 2 million despite it being her 3rd one. "Hard Candy" is Madonna's recent flop in the US which barely sold 1 million.

Ashlee Simpson was my fave

It's sad & frustating but then you're like: come on, who cares! i like this album

Every artist that has 5+ years are going to have at least one disappointment or flop compared to their greatest. Just as long as the music is good to you, you shouldn't feel ashamed of anything.
It just sucks that the people who liked the album know what would have been better choices or what would turn the era around but the label or artist fails to realize.

I can't at the "underperformed" comments