The most impressive class system I've seen in an RPG is in 1992's Wizardry VII: Crusaders of the Dark Savant (as well as its less well-known predecessor, Bane Of The Cosmic Forge). What initially appears to be a straightforward, rigid D&D-style system is given massive depth by two things: the importance of racial base stats in determining class, and a dynamic system that allows for both massive improvement and possible disaster. It's possibly the most in-depth system I've seen in any RPG, and one that I wish was more well-known.
The more complex version is even more interesting. The first step in creating a character is choosing a race. The races are fairly typical for a D&D-style RPG, although with a few more options, like the fire-breathing Dracon or the feline Felpurr. Each race has a base set of statistics. Humans are average all-around, while races like Faeries are physically weak, but quick and smart. Lizardmen are strong and tough, but not very intelligent or personable. An Elf is well-rounded but slightly oriented toward intelligence, piety, and speed, and away from strength and vitality.
Once race and gender are selected, the character's statistics are set. A random number is rolled as the character's bonus. This is the number which can be added to the statistics. Each class has a minimum set of statistics required. The more versatile the class, the higher the statistical requirements. A Fighter requires only high strength and a Mage requires just high intelligence. On the other hand, Rangers, Samurai, Ninjas, and Valkyries demand characters who possess high statistics all around. Those are classes that involve both physical and magical prowess, and skills that other classes can't use.
The bonus is what determines which classes are initially available. The Elf below has been selected as a fighter. From his bonus of eight, the game automatically applies five points to strength so that he can be a fighter. Now you only have three points to distribute.
One option you can use is to take those more prestigious classes from the beginning, although this leaves you fewer points to apply to the character. Alternately, you can choose a class which is consonant with the character's race, giving you maximum flexibility in guiding the character down their chosen path. The high intelligence of the Monk or Faerie races makes them effective mages. So if you select Mage, you can distribute most of their bonuses which will allow them to switch to hybrid classes later.
This is where things get complicated – and fun! Characters in-game have the ability to change classes. This can make them extremely powerful in a few respects. First of all, a character in a new class requires the same amount of experience to level up as a new character. At roughly level 10, the amount of experience points required to achieve level 11 is about the same as the amount required from levels 1-10. Characters also keep their existing skills, spells, and hit points, which both continue increasing with further levels, instead of stagnating (as in AD&D dual-classing). They can also continue developing skills from their previous classes.
How do you improve statistics to switch classes? When characters level up, the game randomly picks statistics to improve by a single point. The number of stats which are improved are random, as are the statistics themselves. You cannot influence this directly, unlike the bonus roll.
The Dwarf Fighter in the image above progressed several levels, and the amount of experience needed for him to progress has dramatically increased. He's also done very well in terms of getting bonuses for his base statistics. His intelligence is a little low, so he doesn't have many options for changing class, but you only need one – in this case, the Monk. So he switches (below).
He still has all his hit points and all his skills from before. But his stats are lower – changing classes reduces those statistics to their class requirements. Not every class has requirements in every stat-the Monk doesn't have a vitality requirement. So that particular stat is lowered to the racial minimum. As a Dwarf, Creigh has a high vitality, and therefore he's still a well-balanced character after his switch.
Yet if he'd been changed into a Priest, however, his stats would have plummeted, because Priests don't have stat minimums in intelligence, dexterity, or speed, and Dwarves have low racial minimums in those, so he's unlikely to progress enough in those to ever be able to switch to a powerful class again. You have to be careful and plan ahead to ensure your characters stay strong.
This is the greatest strength of the Wizardry VII engine. It allows you to develop your characters in any number of different fashions. The most normal method may be to start with six fairly simple characters – two fighters, a thief, and three magic-users, and convert them all permanently to more powerful classes like Samurai and Lords when they can change. Or you can build a party of characters designed to constantly switch to and from certain prestige classes like the Valkyrie or Ranger which keep most or all statistics high as well as fairly even. You could never change character classes during the entire game. Some people have even found it possible to play through the game with a single character!
I've never found a game with as deep or effective of a class system as Wizardry VII. The closest comparison is the Final Fantasy V/Tactics system, which allows you to maintain the skills of your old class after switching to a new one, although it lacks the complexity or potential for failure of Wizardry VII. Even the more accessible sequel, Wizardry VIII (2001), did away with critical components of this system. Wizardry VI/VII stand alone with the deepest, most powerful, and best class systems in RPG history. They're difficult, but well worth the trouble.
Unfortunately, Wizardry's rights situation seems to be complicated enough that they're not available on download services. I live in hope that GOG.com will announce their acquisition soon, and I highly recommend seeking them out on your own if you enjoy deep, excellent RPG systems.
Rowan Kaiser is a freelance writer currently living the Bay Area, who also writes for The A.V. Club, and has been published at Salon, Gamasutra, Kotaku, and more. He still occasionally finds Ultima VI Moongate maps and mantra notes when he visits his parents' house. Follow him on Twitter @rowankaiser.