The campaign is dialogue intensive. Like, really really intensive, we've got a lot of story in there. However, there aren't really any dull moments innit either, you're pretty much required to do stuff all the way throughout, and not just time wasters, but most of the time it's meaningful stuff, and if you're not one to pay attention to two things at once with full concentration it's going to be a choice between paying attention to completing objectives or reading the story, one or the other.
In my opinion, voices are a must for playing, otherwise you'll have to get the order to jump and then press f4 and read back the messages to get a firm grasp on it, which is ****ty. Either that, or you'll be pressing the "restart" button on the mission to play it again and see what was said.
For Ice and Ace, I get why they would want to release without the voices, they've been dealing with BWO far longer than I have, and I can understand them wanting to just finish and be done already, and perhaps leave the voices to the community (like the good job that was done on Derelict).
Personally however, I'd keep it under wraps until all of the voices are finished. I'd want to have directive control over the changes as they occur to the timing after the voices are put in, and make sure it all works as intended, having Ace making the changes himself, since we co-wrote most of the missions. When it's in someone elses hands, you really can't be sure it will be done as intended.
