If I were a woman I would happily bear his children.
He is almost certainly my favorite author ever. I have yet to read something of his that I didn't like.
they seemed strangely believable
I know what you mean, I think its because he has such well developed, believable characters. He spends more time on the people in the story than the story itself, whereas a lot of authors are so busy driving the story forwards that the characters seem like...well, characters, rather than people. Because you can believe in the characters, you have a better understanding of why they are doing what they are doing, so the story itself becomes more solid.
And if you liked American Gods, you'll like Anansi Boys. Best book I've read in ages, and I read a *lot*.
Did you know that he also does a lot of graphic novels too? His Sandman books are bloody brilliant, very...I cant think of a better way of putting it than "grown up". I don't mean that they are all full of sex, violence and swearing (although there is some of that) but the stories he does in Sandman are similar in style to the stories he does in his other novels. Even if you don't normally like comics, I would recommend at least giving Sandman a go, I know several people who consider graphic novels and comics as just for kids, but still like Sandman.