The gameplay is not much different from the previous Blackwell titles, though Rosa's smartphone purchase tightens things up a bit, it holds her notes, lets her look up information online and even lets her make the occasional phone call! It helps to reduce the tedious revisiting of the apartment that the previous games required when Rosa had to do a bit more research.
Rosa has become more public about her sideline of work and seems to have become more accepting that this Medium thing is her calling and that she can't quite get away from it, she has even started to advertise her services, allowing her to help more unfortunate souls. I am not sure that she really needs it though since she seems to stumble across ghosts around every corner.
According to Dave posting on the Wadjet Eye forums, there are still another two to three games left in this story, it will be interesting to see where it goes.