(Sorry it's in Spanish! Fox are dreadful about copyright)
I love the Slayer/Watcher dynamic they have - thrown into nice relief by Wesley - not without problems and growing pains (remember her 18th birthday?), it matures into a really loving relationship of equals that still has a familial aspect. From the beginning he sees how special she is, tries to support her and guard her independence, even to the extent of becoming completely anti-institutional and losing his job for her sake. Who wouldn't want a dad like that? It's an often subversive model of fatherhood (Buffy's birth father is absent and uninterested), placing love above authoritarianism, where Buffy herself is confronted with Giles' past (as Ripper), sexuality (getting over the 'grossness' of grownup relationships) and knowing that grownups often don't get it right. He's comfortable with her sexuality (while there is never a directly sexual dynamic between them), and the show never descends into daddy-protecting-daughter's virtue nonsense. He leaves Sunnydale to let her learn to be self-reliant, but he comes back when he's really needed.
So (to change tack ever so subtly), this sort of subversion is why I think 'Father' language for God is often ok - as long as you have flexible, unessential ideas about gender. This is not to say that it's not unproblematic language, because both women and men can have damaged relationships with fathers/father-figures/priest-figures that make father language difficult if not impossible. Those of us with good relationships with our fathers/father-figures should constantly recognize that privilege and resist reifying father language in a way that is damaging for others. And it's important to remember that we all have women in our lives who display some of the best attributes of 'fathers'.
Janet Martin Soskice puts this subversive element well in her essay 'Calling God Father', where she relies on Ricoeur’s symbolic interpretation of the notion of a father as a way of reading of the biblical texts in which the flexibility of the concept of fatherhood comes to the fore:
Good theology starts with this, the relationship between Jesus and the 'Father', rather than legitimizing and reifying some inevitably flawed, and often essentialist notion of human fatherhood. Balthasar does this in the worst sort of conservative-bourgeois way, and it's insidious in its influence on Roman Catholic theology.What ‘father’ and ‘son’ mean here [in Jesus' calling God ‘Abba’] cannot be read off woodenly from normal family relationships or the Arians would have their case. Rather, ‘Father’ and ‘Son’ function as loaded ciphers, their full significance disclosed only with the unfolding of the ministry of Jesus.
So happy Father's Day, all. Go hug your father. Or someone else's father. Or someone you love. And if you're father to someone else, remember Rupert Giles and be inspired.