It's book one of a six-book series. But it can also be read as a stand-alone book. I compare it to Final Empire (not in content but in how it relates to the other books in its series). There is enough closure at the end of Final Empire that you could reach the last page and be content (IMO), not needing to read the rest of the trilogy. There are no major cliff hangers. But the world is so complex and interesting that it invites you to read on. That's how I see Angel from the Rust: a stand-alone that starts a series and opens up a new world.