1. The new theme.
First i was a little worried, about the new grey colour palette and the reduced colours of the icons. But after a short while i really liked the new design and every time i have to go back to my 8.5.3 Notes client at work i think the old theme looks very dated.
2. The notes.ini variable "TypeaheadShowServerFirst=1"
I really like the "recent contacts" feature, but often it is very annoying that the typeahead prefers the recent contacts over the server addressbook. With the TypeaheadShowServerFirst=1 it notes.ini variable it is possible to change the type ahead behavior to prefer the addresses from the server.
3. The new quickfind dialog.
The new quickfind Dialog is so much easier to use then the old one. I am sure our users will love this feature although there are some bugs in this new feature.
4. The dropdownbox to change the sort behavior of fulltextsearches.
Most users did not find this option in the old client which was hided in the more section. But now this option is easy to find and best off all if you change this option the fulltextsearch order result is changed immediatly.
5. The preview of image attachments in e-mails.
When you get an e-mail with many images attached it is so usefull to see what are the most important images without the need to open every image attachment.