When it comes to RPGs, how many choices are enough to make you feel that you actually have a choice, as opposed to having such an overwhelming number of choices that it is difficult to pick just one? I think that the early fathers of RPGs determined that the optimal number is "four" -- just enough to feel like you are making an informed decision based on min/max stats, preferences, and elimination processes, but not so many choices that you have to mull things over for a few minutes to an hour before you happen upon the best combination for you to play. If you think about it, most multiple choice surveys and tests also have four possibilities to choose from. I will refer to this as the "Rule of Four."
Classic D&D uses this principle, and it's one of the reasons I actually like the system. Choices are few but you feel like you have made an informed choice whenever you choose a race or class to play. By elimating some choices based on other choices you take a possible 16 combinations and whittle it down to a manageable amount. Moldvay Basic took some of that choice away, but in the end the results are not too different.
What more do you need than the basic four classes (Cleric, Fighter, Magic-user, Thief) and four basic races (Man, Elf, Dwarf, Halfling)? You can call them anything you like (Priest for cleric, Warrior for Fighter, Wizard for Magic-user, or Rogue instead of Thief; or exchange Hobbit for Halfling) but those four principle races exist in almost every version of the game from the original to the latest version. What you make of the class is up to the individual player. One player's fighter might prefer to use two-handed axes, light armor, and paint his face and shield to reflect his tribal colors; another fighter might use only noble weaponry, disdain missile weapons, and seek plate mail as soon as possible (as well as a warhorse) to be the stereotypical "knight in shining armor." Both are FIGHTERS, but they are played differently by their players. Sub-classes, which were added later in D&D and cemented in place with AD&D, simply serve to muddy the waters. They are not truly necessary and add very little to the gaming experience.
Now, races have changed dramatically from the original concepts. Dwarves can now be clerics, magic-users, paladins, and various other classes that were off limits to them in the original form of the game. I think that allowing all races to be all classes is fine if that is what all the players desire, but there must be some form of control to keep the demi-humans in check. This took the form of level limits for demi-humans. This is valid if most of the players stop adventuring in the mid-teen levels (say 14-16) and settle down to rule kingdoms. It otherwise handicaps the demi-humans severely. Demi-humans are also the only races allowed to multi-class in the original system, although even humans could have two classes, so long as they only operated in one at a time. Options were limited based on available classes, but all multi-class options were base-classes (except perhaps for ranger, which wasn't official until AD&D).
Now, there is little reason to play a human in a world where demi-humans exist. Only demi-humans gain bonuses and penalties to ability scores, only demi-humans can see with infravision, and only demi-humans can multi-class. So what's so great about playing a human? This was the reason for the limitations in the game regarding classes and levels. I would go one step further and say that only humans should gain the experience point bonus for high stats. I think that the lower limits in the original game were very harsh, but upper levels probably were only just being reached by the initial developers of the game. The higher level limits in Basic D&D and later versions is probably the way to go, with the Unearthed Arcana system allowing single-classed demi-humans to advance 2 levels higher than their maximum if they could have multi-classed and didn't. My current AD&D game has a 6th level halfling fighter running around with 9th-12th level characters in the G-series of adventures and he not only holds his own, he does better than some of the higher level characters! Due to his strength, he was originally limited to 4th level, but when we found the rule in UA, I allowed him to reach 6th. The limitation has not adversely affected his performance, although he is an NPC henchman to the party magic-user and run by that player, so I guess it's not the same.
Lots of pre-generated characters in the G and D-series of modules were demi-humans at their level limit (although some of the levels were in error according to AD&D rules). AD&D and D&D are similar but not exactly the same when it comes to level limits. For example, a Basic D&D Dwarf is essentially a Dwarven Lord at max level (12th), but an AD&D dwarf may be able to go no higher than 9th or so based on Strength. Original D&D dwarves I believe were limited to 6th! Elves in Basic D&D can get to 10th level (the equivalent of a 10th/10th level fighter/magic-user in AD&D) whereas they are limited in fighter in AD&D and may advance as high as 11th if their sub-race and Intelligence qualify them. Original D&D elves could go no higher than 4th in Fighter and no more than 9th in magic-user (depending on ability scores of course). Halflings are generally limited to 4th level as fighter and unlimited as thieves in AD&D and original D&D, but in Basic D&D they are sneaky fighters that can get to 8th level maximum regardless of ability score. In all systems, Men are able to advance unlimited in level (although 36th is the hard cap in Basic D&D). Most campaigns petered out shortly after 14th level -- I can think of only one or two TSR modules published for AD&D 1E that went beyond that level barrier (Isle of the Ape being one, and one of the Bloodstone modules as the other, but there could have been more). A level limit on demi-humans means very little when the campaigns only go on for about 3-5 levels beyond the cap.
The Rule of Four was also carried over to other games by TSR, most notably STAR FRONTIERS. There you have four basic races for characters to choose from -- Human, Dralasite, Vrusk, and Yazirian, with four Primary Skill Areas (their form of profession or class) - Weapons, Biosocial, Scispec, and Vehicles. It's interesting to note that most Fantasy MMORPGs also use this same method when determining roles -- tank (fighter), healer (cleric), melee dps (thief), and ranged dps (magic-user). Adding more than 4 choices starts to muddy the list up with unnecessary roles. One can simply add more 4-choice options to the game to make the permutations increase! This is why I believe the race as class system of Basic D&D never really caught on. It locked the choices to a set of 7 static categories which limits some creativity on the player's part. The race + class options of original D&D, AD&D, and later versions is superior as it keeps choices simple but opens up more permutations.
