Has anyone ever run a campaign in which the elves are not paragons of art and beauty, but grimmer? Perhaps emerging from slavery or oppression?
In my last long-running campaign elves had a fey cast to them, and were chaotic neutral in temperament. They had a huge racial focus towards magics of enchantment and illusion, and while a human visitor might remember an elven city as some glorious glowing tree-city like something out of Lord of the Rings, the reality in the light of day would not necessarily be quite so glamorous, as everything elven would be equal parts glamer and reality.
Even their young adventurers would have often lived for over a century, and regard shorter-lived races with equal parts amusement, boredom and contempt, occasionally saying something tactless like, 'You're still talking? I thought you'd be dead by now.'
The elves of this setting also were infamous for their emotions. When an elf falls in love, it's like a fire that can easily turn into the obsessive and destructive love of a stalker or revenge-killer. When an elf takes an off-handed comment the wrong way, he might draw his sword and attempt to gut his own brother in a red rage. When an elf comes out of such a state, he might look at the bloody body in front of him and collapse wailing and begin physically hurting himself in his grief.
Ten seconds later, that same elf might be petulantly kicking the body, because he just remembered something his brother said fifty years ago that pissed him off.
Humans travelling in the company of an elf quickly learn (if they survive the steep learning curve) to always be on their guard. Their elven companion might be a valuable ally, but he will *never* be trustworthy one, no matter how much he himself might intend to be. He *will* lose his temper. He will petulantly refuse to cooperate. He will laugh at the most inappropriate time and having him present at any sort of diplomatic event or sensitive negotiation is begging for a major land-war.
Creatures from another world, older and less substantial than our own, the elves are physically dissipated creatures, because of their fading ties to an otherworldly fey realm (which they may well be completely cut off from, by this point, or have been exiled from, although neither line of conversation is likely to end without violence). They act slowly, if at all, but react like lightning to events that move them.
In company, elves seem to despise each other, although it's impossible to say if that is true, as they regard concepts like truth, honor and justice as illusory and transitory things, embraced only by lesser races. The only time a group of elves won't be treating each other poorly is when some other unfortunate is present to be the recipient of their withering contempt.
Despite being dangerous and flighty creatures, elves produce some legendary heroes, who become incensed at some moral outrage or insult and end up crusading with inhuman fervor against oppression or evil forces (in some cases for the most unusual reasons). The unnatural strength of their passions can make them incredible forces for good, when their fury rises against an evil agency.
An elven hero will likely have a legacy like that of Enkidu (whose rash acts offended a god and led to his death) or Samson (who was seduced and lost his powers) or one of the Greek tragic heroes, with great powers and deeds, but often brought low (or their deeds tainted) by their own lack of self-control or rash actions.