"Guess what you say?" how is that even pertinent? How would having the lines your character is going to deliver show up when you highlight the choice be better than an older system where your character doesn't deliver any lines at all?
I think people are confused by this system. It is effectively no different than past systems, except perhaps that choices are fewer in any given 'step' in an NPC dialogue and the text that is displayed is much more abridged. The end effect is the same: you cannot say "whatever you want" you are forced to choose between a small number of options for any given interaction. Those options generally seem to amount to (starting from top and proceeding clockwise):
1. INTERROGATION: Give me more information else (occasionally) negotiate. In non-confrontational interactions this tends to open additional NPC dialogue and potentially more dialogue scenes
2. REFUSAL if not DEROGATION if not THREATEN: No, I taunt you a second time. The answer is no!
3. AFFIRMATION, if not FRIENDLY EXCHANGE and in some cases DISCLOSE INFORMATION: Barter, Yes! I'd love to help, sometimes other slightly different options that are neither interrogative, nor refusal
4. NEGOTIATE/BLUFF/"MAYBE"/LIE: The "wild card" slot, which varies a great deal:
A. with merchants it is "Maybe" I presume that giving a merchant this choice and then coming back at a later time/date (perhaps have to make them wait a while) will somehow impact bartering rates
B. In negotiations or "tense" interactions which could result in violence, this choice is used to "bluff" or bargain for better terms.
Other than those four basic choices (and with slight variants in each slot depending on specific interactions) what over choices would people want?
The above structure may not apply to all interactions and it may not be quite right (I haven't played enough to know) but that is what it seems like to me.
I do not see any real substantive difference between the fundamental decision-structure the player faces with the above dialogue system and the older ones. The only difference seems to be in how much of the specifics of the player character lines are shown prior to making the choice and the fact that the newer system is much more immersive. If the actual lines that player characters deliver with each choice were displayed in a popup it would IMHO, add very little to the game, create an annoying blob of text on the screen, and in some cases take away the dramatic effects of the dialogue interactions.
I say this because: I have always found that the choices presented to me in the four point dialogue radial are sufficient for me to know in general if not in specific what my player is going to say. Moreover, because I am a roleplay gamer, I have a strong hunch in most instances of what the possible consequences of the lines are going to be in game terms. It doesn't matter one bit to me if when I choose: "Sarcastic" my PC says: "Ha, you really are a knot head aren't you?" versus "Riiight, I'm gonna go attack a SuperMutant fort to steal back your mother's lucky dish towel . . ." versus "You know, I think you've been taking to many of those chems, cause what you are expecting me to do is insane."
If you choose "Sarcastic" then your PC is going to say _something_ sarcastic! You do not know (for sure) what impact this will have on the game, and you should not know.
If anyone has encountered an instance in which they made a dialogue choice and then found the actual delivered lines were in opposition to the label or description for the choice, then it is not so much a complaint with this "system" of dialogue interactions as it is a complaint that some of the dialogues are badly written or do not correspond with the "choice" they represent and the way that choice is played through the animated lines.
Again, I'll repeat a point I made above: if my intuition is correct, this new system with PC voice, is going to be revolutionary for modding. Alternate dialogue options could certainly be modded into older versions of the game, and one could even have replaced NPCs voice files with alternate voices (I suppose). In this new system, it should be possible to change EVERYTHING!
Once people have taken it apart and parsed all of the PC lines that exist in the game, it should be possible (I hope) for any one of us to create our OWN voice files for our PCs. Want to play a PC that has YOUR voice, and within the restrictions of the existing choices, says whatever you want? That should be possible. I am guessing it will be possible to go a step further, and create a PC with whatever voice you want (or can manage to make) AND restructure the entire dialogue system so that it either has more choices or different choices in any given interaction (although doing that will be more advanced modding operation I'd think).