The headline features see previously neglected areas of RISC OS dragged kicking and screaming into the 21st Century, with JPEG support, monitor EDID support, handling of larger hard drives, and the network stack being upgraded. The bounty system is delivering some really worthwhile enhancements into the software. USB and network stack improvements are a massive undertaking, and ROOL broke each into several stages to make them more manageable.
There are also some genuine improvements to user features such as clipboard improvements and new features in Paint. Lots of applications have received little tweaks such as unicode and fancy fonts in Chars, improved dialogs in Printers, tweaks to HForm, DosFS, Maestro, more secure LanmanFS which can connect to Windows 8 and 10, etc.
RISC OS 5.24 is freely available for Raspberry Pi machines.