I won't bother listing all the changes because that information is available at xfce.org.
I'll just mention a few things that have stuck me in a few days of using 4.10.
The audio mixer plugin for the panel has been updated, and seems a lot easier to set up and less buggy.
4.10 supports a Synaptics touchpad where 4.8 doesn't.
Windows can be tiled by dragging to the edge of the screen.
The application finder has been updated and looks nice. If you have used Gnome 3 and got into the habit of opening an application via a search, the application finder can be a quicker way to find and launch an application than the menu approach.
The biggest change that I noticed in 4.10 was in Thunar, which now has tabs.