As I've played this game more, I've been able to better pinpoint why it's so good.
They focused on keeping the mechanics around the procedurally generated random side missions fun, then layered a story and recurring characters on top of that.
This turns out to be a far better formula for game creation than trying to storyboard the main plot, then figuring out gameplay around that.
Of course at the $25 price point on release day, there are going to be compromises... The "cutscenes" are basically "cutout animation" (static portraits of the characters that the camera zooms in on when they speak). But it works so well in this game, and it makes you so glad they don't waste your time (or their own production money) worrying about what 3D models are doing during cutscenes. It's actually part of the charm of the game that seems low budget at first, but you start to really appreciate many hours in. Especially since it becomes clear that the development investment was made in the distinction between games and movies, where the whole point is to interact with the environment, not watch actors.