Ok, please don't hurt me,... but I just do NOT get the popularity of Gaiman.
I'm not saying he isn't good, I just don't get into his stuff. ;P
To be fair, I haven't tried one of his novels yet, I couldn't enjoy his comics so I never tried his books.
I REALLY enjoyed the first couple of books of Simon Green's Nightside, and his other series as well, Really thought I had found my Dresden filler, but they started trailing off after a few books for me. Both series'. I enjoyed them for a while though, they just seemed to kind of derail themselves for me as they progressed, as opposed to how Dresden Files progresses and matures.
Still, I would recommend that they be given a fair shot. Try them for yourselves. :)