It's funny how almost everybody here tries to compare it to other things. Yes, you can do everything even on paper! Zettelkasten was done first on paper, GTD was done first on paper. But this is new kind of software, which promotes new workflows and ideas about using your thoughts and data, and if you want to compare it to existing solutions then you should compare it to TheBrain or ConnectedText. It's not your typical markdown editor / outliner with some new features - you can start using it like that, but you will change your workflow after few hours or days in ways that you can't simply imagine right now :)
I hope we will have more software with such flexibility in the future, competition is always good, I might even reimplement this myself as my private hobby project, because it's so useful and I can't imagine going back to normal note editors if something happens to Roam dev.