The original series was created in the mid-'90s and covered Vampire: the Masquarade and Kindred of the East, Werewolf: the Appocalypse, Mage: the Assension, Wraith: the Oblivion, Demon: the Fallen, Changeling: the Dreaming, Hunter: the Reckoning, and Mummy: the Ressurection (which doesn't really exist). Each sysytem in the series is pretty much self explanitory, have sub-races and can be mixed together. There were plenty of supliments, but only for details desired by the hardcore gamer or the more creative and dimentional storyteller (dungeon masters for WW), and most weren't pricey, as they were usually paperbacks. The games could be easily played with just the corebook for whichever system you played.
Next came Exalted, which is a pre-World of Darkness universe that draws parallels to the old series, but bore a more DnD-like feel, setting-wise. This game was still excellent and preceeds the sell-out period. Orpheus, a new World of Darkness title that revolved around a scientific experiment to explore life-after-death, was the final core series to be released before long-time fans had their hearts broken.
The New World of Darkness came out in the mid-2000s, starting with a core book just for the human side of the WoD, and currently only covers Vampire: the Requiem, Werewolf: the Forsaken, and Mage: the Awakening. Buy all the suppliments and kiss that college tuition, n00b. No, really; that's how they set it up. And they're all hardcovers. Lame.
White Wolf RPGs are played a level-free system, meaning that points in ceratin abilities determined your ability to do complex actions in the game, rather than being a "must be level 12" fiend. Character sheets, which are supplied in the books, cover these abilities and attributes and allow for a character to be developed on paper more as an alternative identity rather than a character made only for battle and healing. Occupations and locations are mostly free range.
The game is played with pencil and paper and action successes are determined soley with a pool of ten-sided dice, rather than the various sided-dice in DnD. Example, a character wants to sneek past a guard. The storyteller might tell the player to roll their perception and subterfuge, and that the difficulty is 7. The player will add up the number of points they have in subterfuge and perception and roll that many dice. The number of rolled dice that are even or greater than 7 decide as to whether or not the character snuck by successfully and how well or poorly they did. A dice rolled as 1 will damage your results (horribly so if you had no successes), while a 0/10 will cause automatic success or cancel out a 1.
The World of Darkness is extreemly well researched to the point in which it's not that uncommon to see a fan thinking that White Wolf created a DiVinci Code-esque cover up for real were-wolves and vampires, dispite the disclaimer put in each book.
White Wolf also produces board games, video games, novels, and cardgames. The best of the cardgames created by the company is Pimp: the Backhanding, which parodies the Wizards of the Coasts' Magic: the Gathering.