D&D created the standard of hit points, levels, and classes. One of the kludges that AD&D introduced was multi-classing. My own opinion is this grew out of folks uncomfortable with the limiting nature of playing fighters, or thieves, or clerics. People wanted to play an archer, or a magic wielding thief, or a specialized killer assassin or a myriad of other dwarven barbarians, or elf monk ideas they had. In fact one of the remaining issues with D&D is all the variant specialized classes that must be duct taped together in order to play to folks specific character concepts. So classes are in a way limiting to the potential enjoyment of the game and by multi-classing or creating new ones, it may even “break” the game.
On the other hand, a strength of the idea of a character classes is it gives a player a pigeon hole from which to begin the game. If I’ve never played an RPG before a class list lets me pick a clever thief, a ancient wizard, or a battle scarred fighter to start. In addition as a veteran player, if I am exploring ideas for what kind of new character to play, a listing of classes and their description gives me a chance to explore other variations in a simplified format.
Contrast this to the open ended creation of something like GURPS. You need to have some sort of concept of character type before you step into the wilds. Once you figure your stats, then advantages, then disadvantages, then skills you do have a unique character! The issue is the daunting amount of information one must research and know prior to beginning play. For a new player I think it is too overwhelming and it relies on an expert to help guide you in your concept and building of a character to fit that concept.
In the end that’s what character creation boils down to, creating a concept. D&D is limiting in what you can be while GURPS may be too wide open and in trying to provide everything, it becomes overwhelming.
As I work on my own RPG I have taken what I hope to be a middle road of sorts. I do not claim this is unique in anyway, just that it seems to fit into my concept of what makes good gaming. Instead of classes, characters will have a background, maybe call it a career, prior to their current adventuring. This could be anything from wandering wizard, cutpurse, miner, sailor, fisherman, farmer, soldier, town guard, priest, woodsman, or other ideas. I believe this will be similar to the WFRPG idea but it won’t have the idea of migrating into 4 different higher level jobs. The characters had a previous career, then became a full time adventurer. What they end up becoming is whatever they and their GM come up with.
I believe this fills the need to provide a pigeon hole for basic character generation and concept, while allowing a player to become whatever they want through skill purchasing and experience as they play the game.