I enjoy sysadmin, partly because of the variety of problems you are called-on to solve. But the fact is, if you do the job well, and everything works well, nobody gives you any credit. When things go wrong everybody will be looking at you, and if you haven't fixed it within 20 minutes, then you must be incompetent.
So you're the only sysadmin in a multi-campus company? As someone noted up-thread, you can't do it alone. At least, you need someone on each site that can act as remote hands for you, even if that's not their main job. And you need people to delegate grunt work to - repetitive stuff, like building workstations for new hires. That's IT, but it's not sysadmin.
Get some interesting hardware to take home and play with. Stuff like smart switches and firewall boxes (the same gear your employer uses).
GNU/Linux has much better networking tools than Windows; if you're in a Windows shop, get a laptop with Linux on it.
Whenever you do a manual job you've never done before, let part of the job be automating it, so you never have to do it by hand again. Let the automation scripts be the documentation.
Learn to be pessimistic (a common sysadmin trait). If you have bad news, don't ever sugar-coat it. Things might not be as bad as you thought, in which case your reputation is improved. But what people don't want to hear is that the job takes two hours; and then find after two hours that it's a two-day job.
If you can get yourself a full-time assistant/colleague, work as a pair when you can. It reduces stress a lot if you have someone checking your work as you do it (and your decisions). And you end up with two people knowing the systems, not just one.
Get a hardback A4 notebook, and record everything you do.
In theory, you have a lot of power (c.f. BOFH).
You know stuff others don't, and you have superuser powers everywhere. Don't abuse it. Be as helpful as you can. People will be nice to you if they know they might need your help one day. The BOFH was a tyrant, and I don't think he'd get far in a modern business (the BOFH worked in a university IT department, and was God; a sysadmin in a modern business can't behave like the BOFH).*