Remathilis said:
What are the elements you "need" to have a successful campaign homebrew?
Maps?
Gods?
New Races?
New Monsters?
Planes/Cosmology?
What level of detail do you need for a "typical" D&D game? How much do you have? How much is too much?
Maps are nice, but not always necessary to start with. Eventually there will have to be some so players can get a sense of scale and place.
Gods are one of the things I absolutely must have in a campaign setting since I really enjoy playing clerics and characters who pray to specific gods. They have to be really cool gods for me to get enthusiastic about a setting. A pantheon cribbed from real world mythology is cool in my book, but I find most gods of Greyhawk and the Forgotten Realms to be pretty lame, which is a large part of the reason I dislike both of those settings. Along with gods I like to have religions with cool trappings. Also I like the gods to be real gods, not necessarily omnipotent, but still way beyond even super-powerful mortals.
New races aren't something I care about. I know some people can't live without elves and dwarves and all that, but I'd be happy in an all-human world with only the occasional monsters. Humanity can provide plenty of villainy for the PCs to oppose. What you really need are new
cultures. I think that's what intrigues me most about fantasy campaign worlds. Cool cultural tidbits are a major way that I get hooked into a setting.
I don't think new monsters are necessary either. I tend to prefer the classic monster types over the stuff that was made up for D&D (beholders, illithids, digesters). What you really need is a monster palette that fits the world and style of campaign you want to run and makes sense.
Planes aren't necessary, but cosmology is a must in my book. You don't need all those wacky outer and inner planes and stuff, but cosmolgy goes hand-in-hand with having cool gods. What happens to people after they die? Where do undead come from? Where do summoned creatures come from? If there are such things as demons and angels, where do they come from and how do they fit together with the gods? If there are forces of absolute good/evil/law/chaos in the world where do these come from and how do they relate to the gods? These are all questions a good solid cosmology can/needs to answer.
One thing not on your list which is essential, is that a successful campaign world needs is something to hook the players. All of the things you mentioned are different ways you can hook the players. Some players like exploration, maps and new monsters may hook that type. Some players (like me) dig learning about new cultures or interacting with interesting NPCs, new races may hook them.
Also for a successful homebrew campaign, I agree with those who said the setting needs to feel consistent. Otherwise it's difficult for players to buy into it. And it's very helpful for players to know up-front what style of campaign you're running and the general tone of the world.
Now all that is for what I like to see in a successful homebrew campaign world and, thankfully the two I play in have all those elements. Both are pretty generic fantasy as far as what's included, but one is closer to standard D&D in its explanations for everything, while the other has more "If I don't care for what it says in the books, I've got my own reasons for why this is so that fit better with the cosmology I've come up with."
For a "typical" D&D game you can get by with a lot less. All you really need, if your players are willing to forego explanations of where their divine magic comes from, is a dungeon, some monsters and some kind of town/base of operations where the PCs can recover their resources. Then you can add all the things mentioned above as they become relevant. If you are careful about keepng things consistent, gradually a successful homebrew campaign world will grow from those humble beginnings.