I've followed this thread since it started, but I haven't bothered replying to it (wanted to.) Hope noone minds this being revived (again)
First, adeyke's point about puzzle solving & characters was a relevant point. I would only add this didn't apply as much to the Paladin (who was till basically a fighter), and "other" classes added could merely be "bonus" variations of the main three. I don't really think you could really add more than 3 classes in terms of how to handle things. maybe one more, but that would be it. I think maybe Erpy touched on this idea first, though, so maybe I'm repeating mymself :P
Races are a fun idea, but I never got the impression that they actually were a class (sounds like early D&D with "elf" and "dwarf" classes. :P) The only thing stopping Liontaurs from being mages or thieves was generally cultural issues (though a liontaur thief might be a tad, ah, noticable...) Same for a Katta.
Classes should also not be based on solely being a 'hybrid" (IE fighter/thief, "thief/mage, etc" because you can already basically do that (within boundaries.) New classes should add something different.
Shapeshifter would be fun, and could add alot of variety ("Strenght of the bear!" "speed of the leopard!" or something like that) but I'd imagine that animating/drawing it would be a nightmare. :P The only thing I see is that (from qFG) shapeshifters were generally specialized ritual magic, which is kinda not what the QFG Hero-Wizard bothered with on his own. A neat alternative idea might have been to have the Wizard in QFG3 "join" the village and
become a shapeshifter (with the ability to shift between the forms.) That would have added some much needed interest and variety to that game. Though the druid idea could still work too.
Clerics
could work, depending on how you implement it, but you'd have to be careful not to tread on a magic user or paladin. My main objection would be that while Gods do exist in QFG, they tend not to play a very active role in things, especailly solving puzzles :P
Assasin or ninja. Neat idea, but a thief already kinda becomes like a ninja and asssasination could be a thieves skill as well (think Bruno and his knives.) Learning those sorts of skilsl might involve things like smoke bombs or poisons, but again, those could be skills a thief could learn. (Though assasination is rather evil....) The whole "blackjack" thing in QFG 5 was kinda clever I thought.
I do like the "musician" and "performer" idea. My idea was to just call it a "bard" though to stay "traditional", since they were a bit of both. The Bard would be your social interactin character someone who persuaded through words, stories, and music. He'd be very athetlic and able to do tricks like juggling or knife tossing (so he's have throwing.) He might be sneaky and good with ropes (or an acrobat later, naturally.) But not "quite" a traditional thief either. More of a swashbuckler as well, when combat called for. I always figured them as carrying a rapier/sabre and a dagger (dual weapon fighting! Yeah!) They would have magic, but a more sublt kind. Kinda like the calm spells in QFG - ones that influenced emotions or feelings (putting someone to sleep or reducing awareness, changing perceptions or altering emotions, improving the Bard's ability to fight or reducing the enemy's ability to fight, etc.) He also fits in with the "Paladin" idea because Bards would be wanderers as well as a more "heroic" kind of thief. And he could parry, of course
I also like the "Alchemist" or "enchanter" idea, but would combine those as I did "muscician/performer." In QFG its always been the herbalists, alchemists, or enchanters that have been the most "good" individuals (from the Healer in Spielburg and Salim & Julanar, to Aziza the Enchantress and Erana - who created all those magical gardens.) In concept you might think of an enchnater as being like a wizard. But instead of a staff, they used alternate "foci" to boost their spells. An Enchanter implanted spells on objects to achieve effects (scribing runes on walls or floors, enchanting weapons to use the "zap" spell, rings or cloaks of invisibility, etc.) Alchemists used the ingredients/reagents they carried to boost their magic (not just creating potions, but neat powders like the powder of burning which might imitate a flame dart, but also being able to create other sorts of effects.) Kinda like the magic in Kings' Quest 3 - you have "recipes" to uncover and make to create your "items/spells" the items/spells might have certain numbers of uses before losing their enchantment. An extra, interesting twist to spicec up the magic system might be some sort of window or "mini-game" involved in the creation or use of objects (blending the right ingrgedients in the right quantities, like ithe Pharmacy bit in Freddy Pharkas, or having to draw/inscribe the right symbols in the right way on objects to invoke the power.)
Rangers have always been my favorite character, and I'd have loved to be ble to be one in QFG, but I don't think it could work out because rangers (generally) have been very much "hybrid" characters in many incarnations. The Archery idea and the "naturalist" ideas have some merit, but it wouldn't be easy to implement as puzzle solving (or in current combat.) Maybe in combat they might use short swords/large knives (two of them) or a spear instead of a sword (though swords coudl work too - I still like knives though) Maybe give the Ranger the alchemical and enchantment skills. or, even better, combine the "ranger" concept with the Alchemist idea. That would give a good reason to having the scavenge/forage ability - having to find/recover ingredients for spells (from monsters or plant life.) Think of it as a tribute to the Tolkien rangers - Aragorn had "some" sort of innate magic, but mainly with objects or herbs. (Maybe have the Spear double as a wizard's staff..hehehe*) Other possibilities might be to talk to animals or to be able to gain sanctuary at "special" places (like the Dryad groves in the games) Stealth wouldn't be "crucial" but might be a nice touch. Keep hi wearing leather armor in line iwth the "outdoorsman" image.
Scientist would be a "fun" class, though. A joke kind of, but also a bit of a difficulty thing too (wouldn't fight well, can't steal or use magic, etc.) Hard to implement in some cases (can you be a scientist without a lab? Portta-lab? Field scientist?) but it would be interesting nonetheless.
Ideally I'd have tried to keep the game at no more than six characters (3 regualr classes and 3 "advanced/bonus" classes.), but the scientist one might be a fun one (Sorta like the Shepherd in Ultiuma 8, though without sheep.)