I'm a fantasy writer through and through. This was true before I got into the steampunk game, and will be true if I ever decide to not write that subgenre anymore (doubtful, but it's a possibility). Now, one of my favorite (and simultaneously least-favorite) things about writing fantasy is that I get to create an entire world wholesale. But wait, you ask, how can you both love and hate something at the same time? Well, the answer to that is simple:
Worldbuilding is effing hard.
There's a laundry list of factors you have to consider when creating your fantasy world. These include, but aren't limited to, language, history, mythology, religion (which is not always the same thing as mythology), countries, peoples, weapons, level of technology, politics, and social mores.
And then comes what is perhaps the most annoying part of the whole worldbuilding process: Much of the work you do will never be seen by the general public. Ever. To be quite frank, much of the time you spend worldbuilding is only of interest to you the author. And that's the only person it'll ever be useful to. Well, unless you're the next J.R.R. Tolkien, Terry Pratchett, or George R.R. Martin (hey a guy can dream, can't he?).
Let me use an example from my own work. SON OF MAGIC (which is woefully underrepresented in these posts) takes place on a world called Haldor, which is peopled by twelve sentient and semi-sentient races (sentient means thinking, for those who aren't huge sci-fi geeks like Adam, Bane, and me). The eleven races that aren't humans are based off either animals or creatures from myth (yes, there is the obligatory race of elves -- no dwarves though).
There's a total of (I think) 20 countries, each with a culture based off one that currently exists on Earth, with a current level of technology placed at about the 15th Century (the tech level will change when it becomes steampunk). I spent nearly a year concurrently researching and writing in order to get the details I needed for the world, and even wrote a semi-mythical history that stretches back 25,000 years for purposes of the hero. And yes, I do have the ancient race that vanished without a trace. There are some tropes you just can't ignore. *grin*
To give you an idea of the mass of worldbuilding -- I have 20+ files on my computer devoted to this world's backstory, including timelines, legends, organization charts, political relationships, tribal splits, lineages, and capsule descriptions for each of the 15 gods and goddesses. And don't even get me started on how many printouts I have of baby names.
Am I crazy for going through all this just to write a story? Probably.
Am I having a blast and a half crafting new worlds out of whole cloth? You bet your sweet bleep I am.
My theory is thus: any writer who says they don't have an teeny little god complex is a liar. How can you not enjoy putting fictional people through their paces? Or crafting new worlds and new civilizations, boldly going where no one has gone before?
Yes, worldbuilding may stress me out. Yes, it's annoying with the amount of detail it requires. But it's a heckuva lot of fun regardless. And I wouldn't have it any other way.