Painstakingly boring. I don't see any new features or abilities that will change/enhance my experience from 6.2. Since it's a "preview" you can never really be sure if additional features will be added in, but for the most part, it's the same old, same old.
Due to the preview TOS, I can't offer anything other than vague generalities... That said... the much-touted "Photos" is a complete disappointment. Maybe it will run smoother with less CPU/RAM under the hood, but some features from Moments were dropped. I'll be staying with Photo Station if that will be possible. My skeptical take is that Synology is doing away with those Moments aspects that are buggy and too bothersome to recode.
I'm seeing/expecting very little change/improvement in contacts, calendaring, and docker short-comings... Still, RC is well off in the future, so maybe Santa will bring us all nice treats... but I'm not counting on it.
Perhaps our resident optimist will paint a happier face than I'm feeling right now.