Nice writeup -- had been wondering about how it compares to Git (and any killer features) from the perspective of someone who has used it for a while. Conflict markers seems like the biggest one to me -- rebase workflows between superficially divergent branches has always had sharp edges in Git. It's never impossible, but it's enough of a pain that I have wondered if there's a better way.
For me, it's not so much that jj has any specific killer feature, it's that it has a fewer number of more orthogonal primitives. This means I can do more, with less. Simpler, but also more powerful, somehow.
In some ways, this means jj has less features than git. For example, jj doesn't have an index. But that's not because you can't do what the index does for you, the index is just a commit, like any other. This means you can bring to bear your full set of tools for working on commits to the index, rather than it being its own special feature. It also means that commands don't need certain "and do this to the index" flags, making them simpler overall, while retaining the same power.
