We've been shooting stuff in videogames for a long, long time. In fact, the very first videogame was all about two players trying to shoot each other. We've mostly got the shooting figured out, but conversations are still a bit wobbly as a gameplay mechanic. They're getting better, but there's still room for improvement.
For example ...
It shouldn't be possible to accidentally say something.
Here is how it always goes: At some point, I'll miss out on what a character is saying because of mumbling / thick accents / in-game sound effects / ambient noise in the room where I'm playing. So I turn on subtitles. Like most people, I can read faster than people can talk, and so with subtitles on I end up reading the text and then waiting for the character to finish speaking. This gets annoying after a while, so I start hitting the "skip" button when I'm done reading. However, if I happen to finish reading just as the character is done with their line, then the response selector appears just in time for me to accidentally select a response.
A simple solution here is to have different buttons for "skip dialog" and "select response". Another option is to have the conversation wheel default to a neutral position with no default response, so that I must make a deliberate selection before the button will do anything.
It should always be clear what I'm about to say.
I don't know if it was BioWare that pioneered the "summary" style dialog wheel, but I first encountered it in the original Mass Effect. I can completely understand the thinking behind this feature. It's annoying to read all of the possible responses in full, select one, and then have your own character read it back to you. It really breaks the flow of the exchange.
On the other hand, sometimes the summary text can be confusing, ambiguous, or completely misleading. It leads to conversations where you end up saying the opposite of what you want:
JERK CHARACTER: Ha ha! I have kicked half the puppies in the city!
Hm. I don't like this puppy-kicking business, so I'll choose 'outraged'.
MY CHARACTER: What? Only half the puppies have been kicked? Now I'm going to have to go out and kick the rest of them myself!
In BioWare games this is bad because the paragon / renegade system punishes you for "moral" inconsistency. In Alpha Protocol this was bad because the game always auto-saved just after every conversation, thus making the goof canonical.
My suggestion is to sit down with a group of people - you don't even have to be playing the game - and read your playtesters each option and ask what they think would happen if they chose it. Keep working at it until the choices are clear. There is nothing more annoying than having to reload my game because muddled dialogs just screwed up my character.
I should be able to leave the conversation whenever I want.
I didn't even know this was feasible until I played Skyrim and saw how perfectly awesome it was, and now I never want to play a game without this feature.
It doesn't seem to be that hard, either. If the NPC I'm talking to is boring me, or taking too long to get to the point, or if I've accidentally entered conversation with the wrong person, or if they're pissing me off and I've decided I'd rather murder them, then I just hit exit to walk away from the conversation.