Buffy is a realistic show, just set in an unrealistic setting. But still manages to be one of the most realistic shows on television. These people go through things in life everyone can relate to. Not that we go out and kill vampires, but what the characters have overcome and dealt with is so much more realistic and true to life than Dawson's Creek, or any other show. It's also inspiring to many women to see a women in such a strong, leadership role.
It's also daring and exciting. We see so many things other shows are to afraid to let us see. We see what people really go through in life. The choices they must make, and the consequences, good or bad, of those choices. Plus, the writing an acting is IMO far above that of Dawson's Creek, or 7th Heaven, Gilmore Girls, or Everwood, and many many other shows.