I hate to taint "The Harvest" love fest going on here, but I'm going to come in and say that it's one of my least favorite episodes in the series. "Welcome to the Hellmouth" was solid because it had the job of introducing all the characters, and it did that really well. But "The Harvest" needed to take these characters and propel them into a plot that was interesting. Instead we got hokey direction, some bad lines, and a really slow, uninteresting plot.
This is a problem with all of S1, though, to a lesser extent. If I hadn't heard the show got a lot better in S2, I would have never continued to watch it just based on S1. In retrospect, though, S1 is a lot more fun to watch, because all the characters are so carefree, happy, and innocent. It just goes to show how much they grew over the seven years!