It's disappointing when expectations don't match reality. For an artist who wants longevity though, sometimes it's better to completely break from what's expected than try to bend things.
Miley Cyrus is best known for her work as a teenager, but she's not a teenager anymore. She can't just dress in "high heels" or whatever more sophisticated artists do, because you'd ignore that. So she has to do something that will completely destroy her previous work and give her space to be who she is now.
And she's doing just that -- with her music videos, with her VMA performance.
Good artists could play it safe, but they choose not to. They are not here to make us comfortable, they are here to push boundaries and express themselves.
What kind of artist are you?