If it makes any sense, I am fond of both simplicity and choices when it comes to classes. Perhaps because I grew up in a world of the Proving Grounds of the Mad Overlord, but I still think of the must-have classes as Fighter, Thief, Mage, Cleric. It feels natural and it would seem like something was missing if they were removed. However expanding beyond these four is extraneous, at least most of the time. Is a Barbarian really something other than a Fighter? Is a Ranger all that different from a Barbarian? Not really, and nothing that could be tailored into the game with a background and some common sense.
On the other tangent of 'choices', I always liked something to work for as a character. It is a big part of the game to level up, get magic crap, and big piles of treasure. Again, in Wizardry it struck a cord in me to have a character change classes to something beyond what they once were. Prestige classes in 3rd edition did something similar but they had their own bag of worms; I believe in my 7+ years of playing 3rd I can count the prestige classes I used on one hand, out of dozens of characters.
Still, I want to add something for flavor. So with that in mind I will allow all character to be all classes and allow them to use xp in whatever class they want. PC can devote xp to different classes as they see fit and some class combinations will give some flavor name-titles and abilities. I've narrowed the list as follows.
Fighter/Cleric - Paladin
Fighter/Mage - Monk
Fighter/Thief - Ranger
Mage/Cleric - Bishop
Mage/Thief - Illusionist
Cleric/Thief - Assassin
Elf (T/M/C) - Druid
Dwarf (F/M/T) - Stratogineer
Halfling (F/M/T) - Sheriff
Human (F/M/T/C)- Bard
That is to say, only a certain combo will apply to get those name titles. Lets say a Halfling Fighter/Mage/Thief for Sheriff. Should the said character gain Cleric, it would be removed. Secondly I may apply a stat limitation for a said name title; something like a 12 Charisma for a Bard and so forth, although this will be fairly lax. Fluff abilities will be something on par with the racial abilities, that is something to be used in game and though of, but no overt modifiers.
Paladin - Zealous and self-righteous, the Paladin smites his foes with the holy might and clarity of purpose. Valorous and bold, the Paladin is is both a slave and a master of his Lawful nature.
Req : Lawful, Charisma 12
Abilities : Paladins may re-roll a failed savethrows once.
Monk - Mystic warrior who study with forbidden masters and ancient warschools occasionally return more than they once were. Unpredictable and aloof, Monks are both rare and unsettling, never quite at home away from the isolated training grounds they left.
Req: Wisdom 12
Abilities: Monks may cast spell in armor.
Ranger - Often seen as well trained brigands, Rangers are masters of the wilderness, striding with ease where others loose their footing.
Req: Int 12
Abilities: Ranger may use ranged weapons for their backstab ability.
Bishop - Unbeholden to the influence of the traditional Clergy, Bishops wander the lands setting their own holy agenda collecting lore and reason in the world.
Abilities: Bishops may attempt to identify the nature of magical or supernatural effects; this includes items, spells, phenomena, as well as flora and fauna.
Illusionist - Pragmatic tricksters who use magic and shadows to beguile both friends and foes. They are both the joker and the joked upon, as 'true' Wizards discount their petty ways as demeaning.
Abilities: May cast spells listed with a * on their Magic User spells list (Illusionist spells).
Assassin - A super human fighting machine, the assassin is gifted as a spy, a saboteur and a killer. Universally loathed and desired, assassins walk a fine line between life and death.
Req : Non-Lawful, Strength 12
Ability: When hidden in shadows, Assassins may strike while not revealing their location.
Druid - Druids are the keepers of natural lore and the order of the seasons. Compelled to travel to see the world, Druids yearn to wander the years in a new location every day.
Req: Wis 14
Ability: Druids can change their shape to any animal their size or smaller.
Stratogineer - Powerful and possessive, the Stratogineer of the deep workshops hold the might of sway of the cog, gears and steam at thier grasp. Bowing to no one man but to the power of the mechanical alone, Stratogineers tread heavily upon the world in their bronze-tubed boots.
Req: Int 14
Ability: Stratogineers can mechanically replicate any spell they know with mechanical devices.
Sheriff- The halfling Sheriff is prophet, divining the future and setting upon the world to correct and thwart the horrors set in his mind's vision. Ultimately a protector of the halfling people and the world, the Sheriff takes upon the role of prophet and corrector.
Req: Wis 14
Ability: Sheriffs can pregonate certain orrurance in the future.
Bard - Both whimsical entertainer and traveling sage, Bards use dance and music to soothe those around them. Known as true polymaths, Bards seems to have knowledge in just about everything.
Req: Cha 14
Ability: Any intelligent creature listening to the Bards song for a turn or longer will be inflicted by a Charm as the spell if the bard so wishes. Savethrow applies.
These of course will probably change as the setting becomes developed but that is my first inclination. At the very least I need new names for Monk and Bishop. Bards, Druid and Rangers I am not terribly pleased with either. But its a start.