Among the features up for LibreOffice 5.3 are many user-interface UI/UX improvements, new spreadsheet functions, some new templates for Impress presentations, a better OpenXML filter, PDFs can now be inserted as an image into documents, and a range of other work. LibreOffice 5.3 should also offer faster rendering performance and another big addition is the new text layout engine that settles on HarfBuzz for rendering.
More details via the tentative, Wiki-based release notes. The latest LibreOffice 5.3 development builds are available from this pre-release area. The rest of the LibreOffice 5.3 schedule moving forward can be found from this Wiki page.