It takes a while to get used to the interface, because things are layered multiple levels deep. But once you figure out that you can split windows, use tabs or open multiple windows it starts to shine: Have a high level overview of the plot while looking at your character notes, or drill down into your flow and flesh out the details, always while able to easily refer to the notes you made about characters, locations, etc.
This isn't a brainstorming tool per-se, it is a powerful tool that the story people use in actual game development, which is where the export capabilities come in handy - the Excel and XML exports have come in really handy for futher processing.
The pricing is a bit confusing, because this is basically a $299 product split into 3 $99 products (articy draft 1.0, upgrade to 2.x, and a commercial license) but at the same time it means you can start using it for $99 and only spend the extra money if you actually need a commercial license, or if you want the 2.x feature set.
If you're just looking for a tool to draft out a story, there are cheaper alternatives, but if you want to keep track of elaborate plots (think RPGs or Make-your-own-adventure books, or stuff like A Song of Ice and Fire with the many intertwining plot lines) or keep ALL material of your universe (Characters, Stories, Locations, Random Notes, Images,...) together, the software is worth a close look.
As a potential downside, there is only one "flow", so if you're still figuring out your story and have a few scenes that aren't connected, you can't have a "Scrapbook" flow but need to find space in the main flow. The Journey feature might come in at least a little bit handy for that.