The previous response included many important elements, but I think that "The Lottery" has withstood the test of time because of the richness of meaning contained within it. When we discuss this story in class, many possible themes emerge.
One theme concerns the failure to examine ritual and tradition. The people in this story follow tradition unquestioningly, even though that ritual results in a death. They do not even know why the tradition exists. Is that a good idea? How many of us participate in rituals that have no meaning? Is that good?
A second theme that emerges is that of sacrifice. Tessie is the scapegoat, taking everyone's "sin" off into the desert, the original meaning of that word. Or Tessie is a sacrifice to the gods. Are we as sophisticated as we think we are, or are we just as primitive, making sacrifices to have a better crop?
Third, and perhaps most important, the people in the village are decent, everyday people, not all that different from us. Yet they participate in a killing every year. Why does no one protest? What happens when good people do not oppose an evil act? THis is a particularly important question in today's world, in which numerous holocausts have taken place because good people did not speak up.
There are other themes, I am sure, that can be seen in the story, but the important point is that the story has so much to think about, with meaning that is important no matter what the time or place.
"The Lottery" has the status of being a classic because of it's phenomenal use of the literary techniques of irony, suspense, use of setting and plot development. All of these features weave together. For example, the setting uses a beautiful day, sun shining, and children playing. The characters are sweet, laughing, playing and enjoying the day. If things weren't this way, it wouldn't be such a surprise at the end to have such a terrible thing happen.
Likewise, "The Lottery" is successful across generations and cultures. The message strikes humanity equally, it doesn't discriminate. It makes the reader think about their own rituals that aren't necessary.
In the many years since "The Lottery" was written, it has justifiably become a classic. It is full of literary elements such as an incredible amount of irony, it has a wonderfully detailed setting with characters you can believe in, and its pacing and plot fall into an enjoyable read. It also skillfully withholds its grisly outcome until the final few paragraphs, and ends on a note of horror, even though many clues throughout the story anticipate this ending. It is truly a short story horror classic in the genre of horror, though not Gothic by any means because of the wonderful and lush setting of the story.