Second problem: the lack of semantics
Some games take the opposite route: they have gameplay sequences that represent conversation, but that gameplay has no conversational content, or the connection is tenuous at best. You play the role of someone who talks, but no actual exchange that you can read comes out of it. (In other words: ludonarrative dissonance)
This can be, for example, a typical RPG battle system where the actions are given discourse-related names, although what they do is the usual attack/heal/defend, as in The Logomancer. In the best cases, the author's intent may have been to capture only some aspect of the conversation which lends itself better to such abstraction, like tone in Last Word.
There is also the persuasion minigame in Oblivion, and QTEs in the middle of cutscenes in various games, where you have semantic content interspersed with some sort of action, but the action itself - what the player ends up doing - is really disconnected from the content.
A related minority case: games that would ideally be conversations with an AI, which will be very exciting the day that AIs have something interesting to say. Facade falls more on this end of the spectrum, although it lies somewhat in between the two classes.
A stronger example is Argument Champion: it has some semantics, which is quite impressive as it is not at all pre-written but based on semantic analysis (MIT's ConceptNet). It remains a little silly - trying to argue that my audience should like navigation because they like Africa does not feel quite like being Cicero. But it is a step in the right direction, and probably the best that can achieved without a human writer.