Yeah I don't get it. Yeah, her music video's a little.... off-putting, but seriously, she's been repressed by Disney for years to fit their clean, wholesome, family-friendly image... never allowed to express herself up until that point.
I'm not entirely sure if she's truly expressing HERSELF. The very sudden switch to blatant sexuality and public drug usage (coupled with lyrics that essentially brag about it) seems less like she's finally getting to "break free and be herself" and more like she's rebelliously acting out. Pretty much her entire image is focused on said sexuality and drug usage, and her actions at concerts (like the infamous VMA segment or publicly pulling out a joint in Amsterdam on stage) seem like they're based around getting attention.
I don't think the current Miley Cyrus is actually her "true self". It feels like she's trying to break free of her squeaky clean past however she can, and she's overcompensating by going straight for in-your-face adult content. It's like a teenager who smokes and wears black leather and too much eyeliner just to piss off her parents.
This fits in with what I generally know about people who are repressed for their entire childhood and finally allowed to express themselves - they proceed to exaggerate the hell out of everything in an attempt to spread their wings.
That or they hide in their closet because the world is a scary place.
Eventually, Miley will move past this phase of her life, probably looking back with embarrassment.