The show, Buffy the Vampire Slayer, is one of the greatest in history. However, the title, "Buffy the Vampire Slayer," was a mistake for several reasons.
When the television show first aired, I did not watch it in part because it was associated with a bad film, which I did not bother to see. I assumed that the show would be more of the same and, therefore, was not worth my time. I do not know if I would have watched the show anyway, considering that I did not watch anything else on the WB network and often worked evenings at the time. However, I imagine that I was not the only person turned off by the connection to the film. The film got generally bad reviews and would probably have been completely forgotten if it were not for the television show. It was not a good idea to link a new television show to the film.
Joss Whedon has said that the title was to indicate various aspects of the show. "Buffy" suggested comedy, "Vampire" suggested horror, and "Slayer" suggested action. Setting aside the issue that "the" does not suggest either drama or romance, which are other important aspects of the show, this analysis suggests that people see three separate components in the title rather than a single whole. I do not think that most people analyzed these three words separately as intended.
I hypothesize that most people looked at the title as a whole and concluded that the show was a spoof of vampire hunter films/shows. Instead of a serious Van Helsing hunting down evil, a goofy Valley Girl would do so. In fact, this perception may be part of the reason why the film failed. My guess is that when Fran Rubel Kazui, the director of the film, first read the script, she assumed that it was a spoof. Many of the changes that she made pushed the film in that direction and away from Joss Whedon's vision, which was much closer to the show. A darker title might have kept the film closer to the intended tone and would have more accurately conveyed the tone of the television show.
In the minds of many fans, the show is an ensemble rather than a star vehicle. Fans tend to like episodes in which Buffy has a relative small presence to those in which she dominates. In many Internet discussions of favorite characters, Buffy is hardly mentioned. It is not that the fans dislike her, but that they like many of the other characters as well.
A different title would have made it easier for the show to be ensemble. Rather than making one character the focus of 80% of the episodes, different characters can step up in different episodes. In fact, as the show evolves, the best characters would move up and get more of the focus. Furthermore, a different title would ensure that no character was essential. It is not possible to have a show called Buffy the Vampire Slayer without a character named Buffy who slays vampires. However, with a more neutral title, any character could be expendable, even Buffy.
I doubt that Sarah Michelle Gellar regrets taking the role of Buffy. However, the role was very demanding. As the actress playing the title character, she had far more screen time than any of her colleagues. In addition to her acting duties, she also had to do far more publicity than her colleagues did. After a while, she found this to be draining and taking too much time away from her personal life and from other acting opportunities. As a result, she was quite eager to leave the show at the end of the seventh season.
If Gellar did not play the title character, the role would not have been so exhausting. She would not have had to spend so much time either on the set or doing publicity. She would have had more time to spend in her personal life and on other roles. It is possible that she would have been less eager to leave the show after seven years. Even if Gellar still wanted to leave the show after the seventh season, the show could still go on without her.
If I were to suggest a title, I would use one that suggested a location rather than a person. One possibility would be to call the show Sunnydale. It would be a somewhat ironic title as it suggests a bright, sunny location and a show that is probably somewhere between 7th Heaven and Everwood. This would probably solve some of the problems, but it would still be misleading. A better title would be to turn the title of the first episode, "Welcome to the Hellmouth," into the title of the show. Such a name would fit the real tone of the series and would solve the other problems with the title, Buffy the Vampire Slayer. When the show was first pitched, network executives were especially excited by the metaphor of high school being literally on top of Hell. The only problem is that it would prevent a relocation of the show to a place without a Hellmouth, but that did not happen anyway.