Good humor, good characters (even as a dyke Willow is cool, needed better taste in girls), good stories. One of the hallmarks I think was Joss always wanted them to try harder. I’m thinking specifically of the episode Hush, after hearing so much praise for the great dialog and how that’s why the show is great Joss decides they should do an episode with basically no dialog, and they wind up with probably the best episode of the season one of the best of the show. Taking praise as a challenge is a good trait, and it allowed the shows to constantly grow.