This is a scale of the 'otherness' of fantasy settings ranging from 0 -7 that I came up with some time ago . As with any attempt to classify something so diverse and amorphous, it is not perfect, and there may well be some fantasy books that don't fit on the scale at all; however, I still find it is very useful.
0 - realistic fiction, stories that take place in what I term the 'consensus reality'.
1 - our world, with limited magical elements - i.e., no hidden magical societies. Half Magic by Edward Eager is an example.
2 - our world on the surface, but with hidden magic and magical societies - Harry Potter, most urban fantasy. Also, alternate worlds without other speculative elements.
3 - alternate worlds or alternate world systems with open magic - His Dark Materials series, Jonathan Strange and Mr. Norell.
4 - an 'other' world, but one that has clear analogues to ours - the Discworld series.
5 - other world that is not directly related to ours, but still quite influenced by our cultures, past and present - most traditional 'pseudo-medieval' fantasy
6 - may have: uniquely created human cultures, non-human species that are fairly important, humanoid species that are as or more important than humans. In addition to the presence of magic the world may differ in more physical aspects. Steven Brust's Dragaeran novels are an example.
7 - non-human species and cultures more prominent that human ones, the mechanics of the created universe differ significantly from the mechanics of ours.
If a story involves travel between worlds that rate differently on the setting scale, take the average rating, using a rating of 1 for our world - even if there's nothing magical about our world in the story per se, the ability to go from our world to another is. Thus, The Chronicles of Narnia are 3 on the setting scale. Also, a rating may be fractional - I think of Magic or Not?, which has deliberately ambiguous events that may or may not be magic, as a 1/2 on my scale.