Some additional parameters:
Allowed Races: Any humanoid. I'm going to shy away from the "Mos Eisley Cantina" syndrome where you've got all these bizarre alien species in a party. No gelatinous cubes, green slime, dragons, fungus-men, or intelligent octopi. Youve got humans, elves (no drow!), dwarves, gnomes, halfings, and half-orcs. If you want to go a little beyond that, we'll talk (especially if the character you want to play is a monster). If you want to play something "sexy" or "cool," don't overlook the rich diversity in the human race itself (hint: not every character has to be from a Central or Western European-style society circa A.D. 1200.
Allowed classes: All the basic classes. I'm going to write a list of deities shortly. I'll certainly leave the door open for characters to develop into more exotic classes. You also have the option of not choosing a class at this time--maybe your character is a farmer, a smith, a merchant, or a beginning sage, and doesn't want to choose a class. That's fine--we'll work out skills and feats and whatnot.
Characters are mortal. This concept overrides any changes made to D&D by 3.5 rules. No matter how high in levels your character gets, no matter what class, what feats, your character will never gain the innate power to fart ancient red dragon breath, leap mountains in a single bound, raise herself from the dead, transform into a Terminator, take 500 hit points damage and keep fighting, gain thirteen attacks in a single round, etc.
The agenda of the game will largely be determined by the players. I'll certainly throw out clues and hints. But my job as DM is to create the world. Your job as players is to figure out what you want to do in it. You will not be shoehorned into the Quest to Find the Thirty-Nine Parts of the Ancient Scepter of World Domination.