I watched Justice League: The New Frontier again, this time with the first commentary track which features the creators of the movie: Bruce Timm, Andrea Romano and company. I enjoyed it more with the commentary track but it is still lacking.
One piece of information that I picked up (from a Word Balloon interview with voice director Andrea Romano, which I also listened to this weekend) is that quite a few of the voice actors recorded their parts independently of one another. Not only were they not in studio with one another, while recording, some of them weren't even in studio with the voice director. I don't know that much about the animation industry but I've got to imagine that this goes a long way towards explaining why I wasn't very impressed with the voice acting.