RISC OS gets an honourable mention in an (overall) fair review in the current issue of Linux Format magazine (issue 169). They rate it as 2nd (after Raspbian which given that that is the official Raspberry Pi OS is probably fair enough) and give RO a 4 out of 5 star (which isn't bad, isn't bad at all). I mention it just in case you want to give it a peruse.
Only minor quibble I'd have would be over their comments on OS "Freedom" where RISC OS 6 is mentioned for some reason and I believe people unfamiliar with RISC OS versioning might get confused. RISC OS 6 doesn't run on the Pi, is closed source and purchased under subscription (the "Select" scheme) and is (at best) distantly related to RISC OS 5 (it has a different owner and developers from RO 5 as well). RO 5 is open, is available for free download and is (arguably) the version of RISC OS that is subject to the most on-going development.
Other than that very minor quibble - the article is well worth a read.