I do what some people would call "devops", and others might call "system administration". This splits into a number of types of task:

i) routine maintenance & management of running services; this is not very exciting, and lazy sysadmins try to automate as much of this as possible
ii) user support; most of this is handled by helpdesk and the like, but I get some of the more technical problems. Related to this is contributing to technical advice on important issues (e.g. "what does the new weak-DH problem mean for your ssh server?")
iii) dealing with technical debt / trying to improve our infrastructure; this is both tricky and satisfying - you have to balance "what would an ideal world look like?" with what is achievable with limited time, and what you can persuade other people to do
iv) finding, reporting, (and sometimes, patching) Free software. One of the virtues of free software is that we can inspect the code and work out why it's going wrong; I think that means that when we find bugs we have a duty to help the free software community fix them
v) developing new services - this involves research, design, and implementation, usually as a small team (or by myself for small/simple tasks) - I do the automation and sysadminny bits, and other colleagues to the web front-ends