I have a very specific set of parameters and conditions that I MUST see met when I gen a world. If they're not met, the world's no good to me.
I usually go for a 65x65 world, but I'll sometimes try 129x65 as well, occasionally even using 129x129 but not often.
Because I have a hardon for the spoiler tag and detest long-ass posts:
0. A somewhat but not exceedingly long history. I usually go for 360 years, or two dwarven lifetimes. Time enough that most civs are in full swing or just starting to die out and for dragons to grow to a formidable size.
1. Three or more medium sized mountain ranges, at least one of which must be in the world's temperate band. Mountains must not be so large they drown out other biome types.
2. at least 2 of each civilization. That way, if I piss off one group of a certain race, I hopefully still have another to trade with. Also helps reduce the chance of all members of a species dying out before I start playing, as well.
3. Humans(or whatever modded civ creates friendly towns) must have three or more towns and based close to the center of the map. I play fortress and adventure mode equally and need somewhere to buy stuff.
4. Points of interest must be relatively close to the adventure mode hubs. Six days of fast travel just to find the cave I wanted to explore is completely empty is boring.
5. At least one group of goblins(or whatever invader race a mod includes) must survive to the end of history gen. Someone needs to be the bad guy, and I'm not volunteering. Also, two or more necromancer towers, for the purpose of having very bad guys and a source of immortality.
6. multiple small(but larger than one square) good and evil biomes, for me to visit or avoid at my discretion. Evil oceans are right out, undead whales are nothing I want to deal with. Certain races settling inside the most promising of these areas(fecking gobs) is grounds for immediate abort and reroll. Elves and good forests are an exception, let them have it I say.
7. Little or no swamps. Same with deserts, unless I'm going for an all-desert world. I take steps to limit the amount of hills, as well, just because.
8. Rivers, rivers everywhere. Water's always good to have, as long as it's not salt water or an aquifer, or a salt-water aquifer. Most civs prefer to settle on or near rivers, as well.
9. On island/continent type worlds, no volcanoes or caves on one-square islands at the very edge of the map. These are places I want to visit and I don't want to swim across a god damn ocean to do it.
10. Lastly, a large number of megabeasts and semimegabeasts need to survive history gen. I need something to fight between all the goblins or whatever else the modders come up with. (Seems to be a bigger issue when mods introduce races who are individually stronger than the original five, requiring thousands of beasts to be on map for me to see any action.)
After countless rejected worlds, it occurs to me that maybe I'm being too picky about this. I'm spending more time looking for that perfect world to play in than I am actually playing the game. Am I being too specific in my demands for world gen's random nature, or do I need to start using larger maps? What do you think?