In Neil Gaiman's own words (from the introduction), these stories are an assortment of 'curiosities and oddments', including some examples of his earliest writing for comics, and a couple of one-off stories.
The first few are
Swamp Thing stories. I have next to zero knowledge of
Swamp Thing, aside from a vague recollection of seeing that rather shonky Wes Craven movie adaptation some time in the early 80's, so most of the events that transpired in these pretty much went over my head.
However, the last two stories - a John Constantine
Hellblazer short, and a very curious mash-up between Gaiman's own
Sandman and DC's original Sandman character, Wesley Dodds - are both excellent, and are well worth getting hold of a copy of the book for.