As one of the three people you mentioned, damn do I appreciate this. I read American Gods first, and thought it was clever and atmospheric at the time. I still think it's atmospheric, but all the cleverness was merely implied. (If you want good Gaiman, go watch Neverwhere. He wrote it for BBC 2 and it's aimed at adults - I liked it far better than anything else of his I've encountered.) CL&D was flawed, but it was flawed out of ambition and daring. American Gods was flawed out of shallowness - it merely left me thinking "something was very clever there", and when I stopped to find it I realized it was all smoke and mirrors. I wish it would share a bit of it's fame with deeper, more worthwhile books. Of course, I'm biased. Zelazny fits me perfectly also, and I've never found anyone quite like him. Kerouac does sci-fi, maybe. If I wanted to read a great work about flawed and mortal gods I'd go back to Lord of Light.
Most of the point of view characters in Sandman were the same way. He does it a lot. It makes less sense in Neverwhere though, because Door isn't any more alien than most fantasy protagonists. He didn't really need to add someone for you to relate to.
This is very true - I mentioned it because most of his other "cinematic" works like Coraline are aimed at children. I just looked into other novels by him to recommend something, and struck out. Good Omens was a lot of fun, but rather different than his other work. I had no idea how little he'd actually written for adult novels!