The lowdown on bb creams

Ok, so burning beauty question: What exactly IS a bb cream? They are popping up everywhere in stores and in magazines. I must admit, after doing some beauty research, I am skeptical. Bb cream stands for 'beauty balm', which is a product that is extremely popular in Asia. A beauty balm is supposed to have several benefits; it protects your skin from the sun, provides anti oxidants, can plump up your skin with ingredients like peptides, soothes sensitive skin, moisturizes your skin, conceals imperfections, and more. The Maybelline bb cream pictured above is supposed to 'blur imperfections, brighten, Even skin tone, Smooth, hydrate, and protect with SPF 30' according to Maybelline's website. Does it do its job? I have no idea because I haven't tried it. There's something about the American version of the bb cream that just screams marketing gimmick to me. Can one cream really have all those benefits? And it seems like every line of bb creams I come across has a very limited shade range. Boo. I'm kind of dying to try it on one hand, just to see if it works. Maybe I'll buy one and then return it?
  Here's the thing: if you wear a bb cream, are you supposed to stop wearing moisturizer? Does the bb cream function as your normal moisturizer? Or your foundation? Is a bb cream really just a tinted moisturizer? A girl's head is spinning! Anyone have any more theories on these mysterious creams?