Some comments/suggestions:
- The format is good, there's dynamic there, although you're doing reporting rather than having a roundtable discussion. Reporting about what's going on should happen in teaser trailers, which is a much better vehicle for that sort of thing, not a podcast. Having actual discussions between developers would be extremely interesting.
- The idea of bringing in guests from different parts of the design team is very interesting, especially if the topic coincides with what they're working on. As long as there's a stable host (or hosts) throughout the life of the podcast.
- Maybe include an e-mail address specifically for the podcast that people can give questions to. Mailbags are usually pretty dry most of the time, but with you guys being on the inside, the right kind of question could spark a good discussion if there's nothing big going on.
- Responding to an earlier point, I wouldn't recommend adding videos. That's something people can look up in teasers.