The use of variables, both with and without branching choices: Probably the most obvious one, as the success of many VN's seems to depend on hiding the gameplay mechanic from the reader, which would be very difficult to do in print.
Hiding information from the reader: It seems that because the VN format depends a lot on the imagination of the reader to depict events, that the storyteller can 'get away' with hiding information. There are a few VN's I can think of where if it was told as a traditional story or choose your own adventure book, when the big secret was revealed, the reaction would probably be dismay (Why didn't you tell me earlier?) etc...
Time: Flashbacks, past/present reflections or more unusual situations involving time, perhaps because of various artistic/background techniques or programming that can be used to give an impression of this without words... I'm not quite sure of the best explanation as to why this can work so well in a VN...
Multiple perspectives/protagonists: I guess this can just be done in a more understated way than more traditional formats (maybe a comparison could be made to a print novel based around an exchange of letters)...
I'm interested to hear what other people think, it's likely that some of what I've said is completely misguided.
Ignosco


