Hi and welcome!
The patch includes nearly two years (since game launch) of continued improvements: bug fixes, new scenarios, new rules, new graphics, lots of AI tweaks, tons and tons of historical and flavor added content, new game features added for free...
The game now is a lot better than it was out of the box.
The patch has more new content than many pay expansion aroudn.
You should update it without any doubt
Just take a brief look at this loooong readme file i attach you here with all the patches changes since launch (all included on teh last one)
Beware... its 36 pages loing!
(36 pages of free added goodness! :coeurs
Regards