This JSON Web Service example page includes this release request: http://musicbrainz.org/ws/2/release/59211ea4-ffd2-4ad9-9a4e-941d3148024a?inc=artist-credits+labels+discids+recordings&fmt=json
If you compare the result from the example page and the actual real result, you see that the part "release-group" including the primary-type is missing.
How can I retrieve a release including it's primary type (and other types if existing)?I'm looking for the information like "album", "compilation", "EP"...
You need to include release-groups, obviously; releases don’t have types. (Yes, it's a documentation bug.)