This is expected to be a major upgrade from the previous version, Snow Leopard which had mainly performance enhancements. People are speculating that Apple might eventually merge their iOS with Mac OS X and this might be the last version of the desktop OS.
Well, with Apple, you can never be sure. The entire world expects something and then Apple comes out with something totally unexpected.
I am going to be keenly awaiting the October 20th announcement. I have been using a Mac for years now and am really excited to see what Apple has in store for us! They have revolutionized the phone and the tablet in the last few months. Let's hope they have something equally great for the desktop now.