I've been trying to read a long Giles/Oz series of stories that I saved to my Macbook before leaving, and utterly failing. I think the core of the problem is that in this story he is gay, and I do not read Giles as fundamentally gay. I don't see him as that Kinsey extreme. Or either Kinsey extreme, to tell the truth. I see him as bisexual. Or maybe toward the het end, with some intense affairs with the same sex now and then. I cannot ignore the canonical affairs with Jenny and Olivia (and the fling with Joyce).
I do know that fanfiction's purpose is to stray from canon in these ways, and I damn well hope that authors take these characters in the directions they want without worrying about my opinion. I can just skip the stories as "not working for me" and move on to something that does. I was just noting my reaction, which surprised me a little until I figured out why.
This explains why some other Giles stories haven't worked for me either. I read a fairly hardcore short series a while back that had Giles doing watersports and leather and getting a guiche and then dumping Buffy as his Slayer entirely. This story didn't sit well with me, and now I understand why. That author's Giles wanted nothing to do with women, and the Giles in my head likes them just fine. (Though I confess to not being able to cope with watersports personally. Piercing kink works, oh yeah, and I may write that for Giles some day.)