The specifics of the obsmode improvements aren't well documented in the patch notes. Here are the big ones that I noticed today:
- The minimap is much bigger!

- The wrong-color-VP-bar bug is fixed

- The graphs (army, float, territory) scale to higher amplitudes so info isn't cropped

- The UI scales perfectly w/ the center control box & no longer overlaps the commander cards

- There is a new "Ctrl-G" hotkey that toggles the unit shields display
might be useful in big teamgames
It seems that we still can't see "all chat"

and I'm not sure if the UI tells us who won at the end of the game or not. I haven't gotten a chance to test if the "observer mode party" unit slowdown bug was fixed. I'll update here when I know more.
Overall, I'm thrilled. Having a bigger minimap and a properly scaling UI is huge win.