It's epic fantasy - the whole of humanity is ruled over by an immortal tyrant & the story is mostly told from the perspective of Vin, a 16 year old girl who turns out to have special abilities & becomes a part of a plot to bring down the Lord Ruler. What sets it apart from other epic fantasy series is a unique world (and magic system) and a story that reminds me more of "The Lies of Locke Lamora" than of the "The Belgariad". And it's also set a thousand years after the end of an epic fantasy type story - the chapters are all opened by little snippets from this previous hero's diary. (And worth reading, I often skip stuff like that, but these add to the story).
The magic system is one I've not seen done before - an Allomancer "burns" metals (either pure or alloys) that he or she has swallowed and different metals give one different abilities. For instance burning brass will allow you to manipulate other people's emotions. Most people can't do this at all, some people (Mistlings) can burn one of the metals and a few very rare individuals (Mistborn) can burn all of them. Vin has been utilising trace amounts of metals that are naturally in her diet/water without knowing what she's doing, and she attracts the attention of Kelsier who tells her that she is a Mistborn (like him) and teaches her how to use these metals.
Society in The Final Empire is very stratified - there are the skaa and the nobles. They are regarded by the people of the world as two different races, and I'm not sure how much that is truth and how much of that is fabrication to justify the brutal slavery that the skaa are kept in. There is definitely something that the Lord Ruler fears tho, because one of the strictly enforced rules is that there should be no cross-breeding - so if a nobleman wants to have sex with a skaa woman then he must have her killed afterwards to ensure no offspring. Obviously that isn't always how things work out.
Vin is half-skaa but lives as skaa & has been part of a thieving crew for most of her life, since her mother went mad. These crews are what reminded me of "The Lies of Locke Lamora" - particularly after she joins Kelsier's crew. The plot to bring down the Lord Ruler is partly a con-job, and Vin is groomed to play the part of a provincial noblewoman visiting the city for the first time. She's had a pretty abusive childhood & over the course of the book you see her growing from that shutdown/closed-off child to a more well-balanced young woman.
One of the things I liked best about this book is that once you get to the climax there are revelations that knock sideways the way you perceive what's been going on in the story so far. A bit like a kaleidoscope - it twists and suddenly you see a different pattern. Some of these are personal to Vin, some are more global, and I think it's going to be interesting on a re-read to see how it's set up once you know how the pieces are going to fit together in the end.