All Hallows' Eve, or Halloween as it's currently known, was originally a handful of other holidays. A harvest festival, a day of remembrance of one's ancestors, and a night when spirits rose from the otherworld to walk the world of man. These days, it's hard to separate the original traditions from the modern consumerist trappings, but you still see echoes. People dressing in costume to confuse the spirits, decorations that include skeletons and ghosts to honor the dead, food and drink to celebrate the harvest. Elements of Walpurgisnacht also turn up, but that's actually an entirely separate holiday, mostly celebrated by witches.

As for pumpkin spice... I have to say that I agree. It isn't something I care for.