I Like it, I like the fact that you can instantly enter the game and i also like the whole Gold/Renown/Experience thing xD
I Also like the camera angle its different from the regular split screen
To Me Co-op birngs much more to the game, as in some games co-op is needed to get certain achievments etc but that may cause some hassle.
People keep stating Co-op is nothing new, I disagree Co-op for different games means different things such as :- In Halo that Co-op for that would be much different than the Co-op for Fable 2.
In Halo you would just probably team up and kill peeps or Kill each other xD
In Fable 2 you have a nice diversity/variety of things you can do in Fable 2 with Co-op, this includes levelling together, making money together and probably even raising a family together (Dont know for sure) But Co-op brings many different things considering the Genre of the game and the actuall game style itself.