As I think about it, I've decided I need to make my reply more *useful* than "Go for it!"
I like audio books.
I like the pure audio drama.
But the GraphicAudio format, which I will now refer to as "dramatized audio books" is my favorite for the following reasons:
1. Inclusion of a narrator.
...I don't always interpret clearly what a producer is intending to convey through pure sound FX. The narrator's commentary makes clear the sounds of battle, and gives meaning to "hah!", "ugh!", and "oof!" Without having the participants narrate for me. (ie, "Oof! You hit me in the gut!", or "Hah! I absorb your attack and blast it back at you!") This is a convention that removes me from the story because meaningful dialog *never* follows this pattern, whereas the convention of a narrator is a familiar part of oral and written storytelling.
2. Separation of cast and narrator.
...Not everybody does "voices" well. And of those who do, only Frank Welker and Mel Blanc have ever managed to cross the gender line for me. I greatly appreciate have a different voice for each member of the cast. Even if some of those actors do multiple roles, the context separation is important, and makes a difference for me. I find it disconcerting to have the narrator poorly and inconsistently voicing characters. Even when the narrator is doing a good job, gender, age, and ethnicity differences among characters never seem to translate well.
3. Music and sound FX.
...While I prefer not to rely wholly on these vehicles to convey mood, action, or emotion, I do appreciate the value they add to a production. A driving score behind an action narrative, the rumbling bass of a .50 machine gun, or the unique sound of magic all contribute to the ambiance of the story and increase my involvement - by giving me something to which I can relate the narrative.
4. Continuity of story and involvement.
...Pure audio drama is fantastic! If I can listen to it all in one sitting. If not, well, I lose a lot of the story details and momentum between sessions. By having the narrator explain what is going on, it provides an immediate context in which to place the ongoing story, action, and dialog. Without this context, I struggle to get back into the story and reconnect plot points, character identities, and emotional involvement.
And that's my opinion.
By the way, long before GraphicAudio was around, some of you may remember Peter Pan and Power records were doing some pretty awesome stuff with dramatized audio books. I know we tend to think of that as "for kids", but a lot of their stuff still holds up and is entertaining for adults. Conan the Barbarian, G.I.Joe, Batman, and Superman all come to mind.