Randomthoughts
Adventurer
I enjoy running a game. It's an improv performance that I find very enjoyable, depending on the group. I don't GM long if I didn't enjoy it. But preparation is involved.I actually like running a game and look forward to it. Am I missing something? Do others think of it as a chore? Do players assume the GM isn't having fun?
@Umbran describes my view on preparation, except that it is often fun (not just sometimes). The amount depends on the game but for 5e - a system I'm learning "for real" - there is a solid amount of it.
@BookTenTiger describes the other part of prep. Most of it is done either in my head or on my laptop using mapping and graphics software and the VTT. A lot of it isn't necessary. But when I have an idea in my head, I want to create it somehow (hence, I got into Dungeondraft and Hex Kit). I also enjoy researching direct or tangent topics, for mental background before running a session. Again, not necessary but enjoyable.So, I don't think "fun" and "work" are mutually exclusive, so I am not convinced if you're asking the question in as useful a form as you might..
For me:
Preparation is always work. It is sometimes fun.
Organizing people, getting things scheduled, and hosting a game is always work. It is rarely fun.
Running a session is usually not work. It is usually fun.
Preparing for the game I consider almost a separate hobby. It's very personal and independent, and what I do with my cup of coffee on a Saturday Morning instead of reading the news. Although a lot of my prep happens in my head on my bike ride to and from work as well!