I've been a long-time user of Scrivener, and what can I say — V3.0 is an amazing amazing update. The underlying philosophy of Scrivener is to help you organise your material while writing (Binder stores everything in one place, easy to search through), and separating how the work will "look" to a final phase called compiling.
V3.0 has a powerful new styles system, and many many changes to compiling. For example you can now use styles to semantically/visually identify "blocks of text" (e.g. a quotation). During compile you can transform this into many different styles — even using plain text markdown transformations. There is a new Section Type, and each section type can have a specific format (page breaks, font etc). So you can customise from the same project specialised outputs optimised for EPub / HTML5 / DOCX / LaTeX and many others.
There are many more changes, including custom metadata types (like dates), unified bookmarking, a cool new copyholder UI, snapshots manager and everything is faster and "flatter". For existing users of Scrivener, many things have changed and you should really have a look at Appendix E of the new user manual and the L&L blog posts about V3.0 (the user manual is made in Scrivener>MMD>LaTeX and it gives you an idea of how flexible Scrivener compiling can be).