Here is a nice little preview of what to expect from the co-op (local and online) and boss (using any mobile device using smartlgass as a third player) modes:
The smartglass integration sounds pretty fun actually. In fact, it reminds me of the gaming options that we have seen using the WiiU tablet controller. If it works as described, I can see that being great. It would also demonstrate what is possible using smartglass, which is certainly needed.