Given Valve's track record, I think that any information given about the G-Man will be so cryptic that it would only fuel speculation. I don't think there's anything wrong with G-Man discussion in and of itself, it's just the unoriginal or just ridiculous theories.
It's one of my favourites. The Half-Life soundtracks are great. I love how even when the music uses more traditional instruments, it still has a distinctly alienating feeling to it.