'Changeling: the Dreaming' is one of the finer games from oWoD, and ranks with 'Mage: the Ascension' as one of my core games to run. I'll take any opportunity to run or play this system, and this serves as an excellent back-up copy for my well-worn print copy. The only downside to the PDF is that printing this out will be expensive if you want to do it in full-colour glory it richly deserves.
The game centres on Changelings, part human, part fae, who try to straddle the grim banality of our world but not over-indulge in the fantastic world their glamour creates. Each type of changeling (known as a 'Kith') hearkens to a particular human ingrained in the collective human unconscious. The Sidhe embody the all we know of honour and beauty, Trolls are noble protectors, whilst the Sluagh are the un-nerving whispers in the shadows.
The culture is well-developed and offers many levels of play, and plenty of opportunities for very different genres, moods, themes and ideas to be explored.
The core book offers all you need to play, and has a module in the back to get you started, as well as introducing the major players in the 'Immortal Eyes' chronicle.
For those preferring nWoD lines, you can explore 'Changeling: the Lost', but I'd highly recommend reading both as I've found a lot of cross-pollination between the books that will improve your game.