While I am not in favor of full voice for RPGs with a lot of PC dialog, it's only because of the conversational limitations that would impose. In a text response game, the dialog can change or be expanded late in development, or even be changed with an official patch ~without requiring the voice artist to re-record the lines. Aside from that caveat I do like it when the developers cast a good voice actor. I have yet to play an RPG where the voices I could pick from did not have a (pleasantly) acceptable choice; or where the one I was given was not fine by me. I'm fine with Arx Fatalis and it has just the one voice for your PC (and only four faces to choose from ~and in all this time, I've still always picked the same one).
The only real negative I see (assuming they were able to do full voiced on par with full text based), would be that for modders, the game causes the expectation in the player that everyone will be full voiced ~and so custom NPCs stick out like red painted elephants, and custom scenarios will rarely if ever involve voiced dialog with NPCs from the official campaign.