Is this a new idea? As far as the overarching plot goes: no. As others have pointed out, from Dune to Harry Potter, Vin comes from a very poor background, gets kicked around a lot by the people who are "taking care" of her, and then learns she is "the girl who lived" basically, with a lot of powers that she quickly learns and uses against the Lord Ruler, the guy who has ruled the whole world for about 1,000 years and survives minor things like beheadings and stakes through the heart.
Why then, give this book five stars? One: this is a trilogy and we've taken care of at least one pretty bad dude by the end of book one, so that's not going to be a continuing theme. Second: this writing is straightforward and fast-paced. I liked that Sanderson didn't make us guess about how the metals worked; as Vin learns how to use them, we learn along with her. Sanderson keeps us guessing about a couple of things, but we're not generally left wondering "what the heck just happened" unless Vin is in the same boat.
Sanderson is great at making characters. In Vin's little band, we have Kelsier, his brother Marsh, Sazed, Dockson, Clubs, Breeze, Ham, Spook and Yeden. While his language is straightforward and relatively bare bones, I was never confused about who was talking or what each person brought to the group. Each one had a distinct personality without anyone being a flat stereotype.
The world building was detailed and amazing. Besides those who are able to burn different metals for different powers, we are in a world where giant volcanoes are constantly belching ash into the sky. Nothing is green. Staying clean is a luxury. And he has set up a caste system with the skaa as workers dependent upon the nobility for food and shelter, while in turn the nobility are dependent upon the Lord Ruler for place and power. Both the nobility and the Lord Ruler see no problem in cleaning house through slaughter when the mood strikes. It is a system that has been in place for 1,000 years under a single ruler. There's also the mist, that the skaa have been taught to be afraid of. The mist only comes at night and it is clear through the story that the mist has not always existed, just as the volcanic ash has not always existed. These core, but less pressing mysteries, along with the characters are what will keep me going through this extremely dense series, with pleasure.
As an aside: I think that hype is picking up on a book that was first released 12 years ago, in part because word of mouth is spreading. This original cover and subsequent covers have been unfortunate choices in an era where cover art in YA is more important than ever.