What I think is incredibly cool is not just the simulation of a single system, but of an entire network, the environment the networks ran on, and the historic "feel", with fake users, nodes, hacking tools, games, interpreters, random files spread all around.
It's one of the most incredible things I've ever seen.
I'm half wondering if it's possible to mirror this in some way so it can be preserved for posterity..."telehack in a box" or some such.