1) It will offer some type of unique three-dimensional or at least multitouch interface and experience that goes beyond what's currently available on the iPhone. (See my earlier blog post on one of Apple's latest patent filings on 3D tech.)
Why do I think this? Because Apple's not the kind of company to be content with simply "scaling up" their Tablet to simply be a larger iPhone, or a clunky finger-swiping iteration of its OSX/Leopard environment. When they enter a category, they play to change it completely.
2) It will offer cloud-based computing in a way that will be a big step for Apple. It will be able to stream more and more content and you'll be able to sync it with various Apple applications and perhaps even non-Apple apps.
3) I predict it will come embedded with some type of sophisticated image-recognition software system, where you can use the camera for various tasks, such as searching for objects you photograph and looking for information connected to the object online. (Not sure what I mean? Take a look at LookThatUp.com, by LTU Technologies -- a French company that one of Apple's product engineers used to work at.) Perhaps you might even be able to use the camera as a virtual joystick for controlling actions and apps on the Tablet.
What do you think? Follow my tweets at @gussent.