It uses the 3270 terminal (xterm has a 3270 mode I've used), interface is predominantly 'ispf', it's essentially menu driven; you can browse/search the filesystem, edit files, submit jobs (everything is a job ie jcl ie job control language; compile, run programs etc) browse job spools (stdout from a job).
Google will show you images of ispf, browsing the jcl manuals will give you nightmares.
It is not terrifying per se, just ... very different.
I have only had brief contact with JCL, but I remember having to figure out how to get a command line into JCL that was more than 80 characters in length. It took me two days to figure that out, and none of the old-timers in the team had ever had to do that. When I did find the solution, it was surprisingly simple, but finding it took me a lot of time.
Google will show you images of ispf, browsing the jcl manuals will give you nightmares.