I work on z/OS utilities, mostly assembler. It can be fun, you have to be resourceful. z/OS is actually quite pleasant environment compared to many newer platforms (such as Windows), because you get a very high visibility into what's going on in the system.

I guess it depends on type of person. If you love to understand things across the stack (what's going on under), you might like it. If you would rather focus on an application (or framework) layer only, you probably won't.