In the beginning of RPGS, dieties were viewed as really big monsters. The information given was nearly devoid of any information on how to actually use the deity in the campaign.
The reaction against this resulted in elaborate mythologies of near omnipotent gods. Yet largely devoid of information how to actually use this in a referee campaign. In the first case the wrong information was given and the in the second the information was on too high of a level.
It has gotten better over the years but still not enough is done. The 4th edition deity description are fairly good at giving the player the needed information for being a follower. But they lack information useful to the referee like typical temple layout, information on the how the priesthood are setup. Granted this is understandable as they are in the Player's Handbook and space is limited.
When detailing deities for your own campaign. I recommend more work be spent defining the religion not the diety. Along with what the followers believe, define how the temple are laid out, what are the important dates, and what type of hierarchy they have. All of this information is pertinent when creating adventures involving minions of that deity.
Don't get me wrong, some minimal mythology is needed as it is often the foundation for their beliefs and movitation. A good guide I found is to limit myself at the beginning to about a page worth of information (using a 10 point font).
For example when I worked with Necromancer Games this is my entry for Thor.
Thor, Battle God of Lightning and Storms, is Neutral Good. Thor is a major god in the court of Odin and in the hearts of many more popular than the All-Seer. He is known for his many heroic deeds in saving his worshippers from the depredations of monsters and giants. He eagerly rewards any follower who is willing to undertake similar quests. His domains are Air, Good, Strength, and War. His favored weapon is the Hammer. He is revered by the Skandians has shrines and temple scattered throughout the Wilderlands. Many of his clerics use the Temples of Odin as a base in their quests against the monsters of the Wilderlands.
I was limited in space so I didn't get into the details of the temple and the hierarchy. My goal was present, in as a few words as possible, a deity who was the patron of monster hunters. That they were so focused on the task that in many places they didn't have the time to build temples of their own and thus worked out of the local temple of Odin. That he was a popular among the ordinary folks which means PC who follow him have a leg up in trying for a good reaction among the peasants and townsfolk. I left out any combat stat information and only inserted the bare minimum of high level information.