Thanks for trying out the new REST api!
With 4.2, we shipped an alpha release of our new REST API, which includes mostly read APIs for individual issues.
We continued to evolve the REST API in 4.3 and 4.4. We published the REST API documentation for 4.3 and 4.4 releases here:
In the JIRA 5.0 release we plan to take the JIRA REST API out of beta. As always, we would love to hear your feedback and comments about this feature. To keep the discussion centralized (both past and present), feel free to comment on this issue with your feedback.
Please note that the JIRA 5.0 version of the REST API has changed significantly from the alpha and beta API from previous releases. The JIRA 5.0 API goes well beyond the read-only API from previous versions. The new REST API should include create, update, delete, search for Issues and manipulation of individual issue fields.