White Wolf has been the leader in the current major wave of change to take the Role Playing market. Initially TSR evolved Dungeons and Dragons out of simple Chainmail arena combat style rules--the earliest dungeon occurring when Dave Arneson decided that a maze with traps and monsters was far more interesting than just fighting them in an enclosed area. The images of what player's characters were doing when they were not fighting led to Roleplaying. For the entire early history of my roleplaying hobby the games have been dominated by the 
level-based system due to the attempts of many to compete with the power of D&D. This was to change,however. 

The earliest breakaways from the level-based system that I remember were Runequest by Chaosium and The Fantasy Trip by Steve Jackson. Each of these systems featured skills as being the major facet of character development. The character could excel in some extremely limited areas and be dismally unskilled in others to a degree never possible under even the Rolemaster level based system. Combat ability depended upon the ability to strike your foe and block his blows, instead of relying upon some strange system of hit points. Unfortunately 
The Fantasy Trip always seemed like a ripoff of Dungeons and Dragons and Runequest just never completely took off and eventually Runequest was sold to Avalon Hill to finance Chaosium's continued production of their true masterpiece, Call of Cthulhu. 

The next link in the evolution of Role Playing games towards White Wolf's Storyteller system was ShadowRun. The creation of a success-based skill system allowed more skilled characters rules to cover varying degrees of success as well as a greater chance of success. The Health track also came into being. ShadowRun preserved the idea of a point based creation system that had come into being through The Fantasy Trip and later GURPS, but it also expanded the Character Class concept of Dungeons and Dragons into the Archetype Concept. The stage was set. 

White Wolf's Storyteller system drew upon a wealth of experimentation and success from past games, including their own connections with Ars Magica. I have always felt that ReinHagen saw the game Nightlife and thought, "I can do better!" Players became able to play the Monster, to explore why evil and good are not really black and white images, to explore their humanity by becoming Myth Personified. This is the real secret to White Wolf's setting, of course... that it taps into centuries of superstition and stories of the supernatural. Even the unbeliever 
like myself cannot help but feel some attachment to the mythic elements being discussed, for we have been immersed in them all our lives by everything from fairytales from childhood to Hollywood Blockbusters to novels and comic books. These are mythic elements with a powerful window into our psychology--the lure of immortality, the dark sexuality of the vampire, the primal emotions we feel that lurk within like a raging werewolf, the desparate desire to want our dead relatives to still exist in some form even if only a nearby ghost, the childhood visions of beauty that explain the yet unknown with personified nature. 

If the success of the White Wolf World of Darkness setting is owed to its mythic element, the success of the Storyteller rules system is its adaptability to translating different visions into a game that can become as simple or as complex as the players and Storyteller desire. It contains a powerful core system that glides easily from one shell to another. The fact that a character pairs an Attribute (describing innate characteristics of the character such as Strength or Intelligence) with an Ability (the various skills of the character) gives an additional element not really seen before except in Ars Magica. The Nature/Demeanor traits encourage roleplaying in a powerful, ever-pervasive, yet somewhat subtle* fashion. The Experience Points system is realistic in its demand that the character only be able to spend experience upon skills which his character could have learned during the game, to 
plan his advancement by roleplaying as well as numbers crunching. Additionally, the long sections on Storytelling add repetitive drive to roleplay rather than roll-play. In fact the very name "Storyteller" is subliminal suggestion to make your game an effort to tell stories.  

My favorite of the Storyteller games has always been Mage: The Ascension. In fact, I did not play Storyteller games until the Mage game grabbed me and said to me that here was a great system and setting, to explore it and see how the other games compared. I was hooked, and I discovered that I loved them all. I have run combined games and pure settings alike. It pains me deeply to see the vicious flame wars that plague White Wolf newsgroups fighting over which of the White Wolf creations is more powerful or more interesting. That is a personal decision for each player and each storytelling group; if you love vampires, they will likely be the most potent force in your game, or if werewolves tickle your fancy, then the Changing Breed will certainly be waging the Just War at the expense of the kindred. I honestly don't care which faction is the most powerful. It is not yet settled in the game setting by the principals involved, and if it becomes settled by the opinions of others then whole elements of the setting have been lost by predetermination.  

As I mentioned, Mage: The Ascension has been my favorite of the games. I was immediately struck by what I think is the best magic system ever developed in any role playing system that I have ever seen in my entire life. It is of course an incredibly demanding job to live up to the magic system's potential--depending upon strong role playing and intense effort to manage one's use of magic in such a way that the story image of the magic is colored correctly according to one's Tradition and beliefs. The simple, yet infinitely variable, system of performing magic is unique. No other system gives one the flexible power to perform magic so unrestricted whilst still maintaining balance. The tough part is that the system itself devours so much of the rulesbook that players who are unwilling to do the research often drop into game terms even when speaking from their characters' voices. However, groups who are willing to restrict their characters' use of magic to what they should do given their beliefs and Traditions, rather than what the rules say they can do, reap enormous benefits in individualising their sorcerors and being given the opportunity to endow them with exactly the flavor they should possess. You are unharnessed from some strict rules of magic that prevent you from creating the theory of magic under which your character operates such as exist in every other game with magic. You are free to explore what your mage should do, rather than what he can do, and that is all the difference!!!