Am I the only one who thinks Konami made a huge mistake in making the Act 1 Mission Briefing not part of the game, making the player leave the game entirely to watch it? I mean, I never knew it existed until after seeing the Act 2 briefing and wanting to go back in and explore it some. A friend of mine also missed it, and he almost stopped playing the game because he didn't understand anything that was going on. I bet most people playing the game won't dicover it at least until they are finished with Act 1; heck, I saw in this thread a couple people who didn't see it until after Act 3!
The briefing gives a good backstory for the game, tells you why the heck you are there, and is useful even explaining little things like what "PMC" stands for. The fact that the briefing is missing from the game (and especially that it has that "egg" scene which just seems to not make any sense without watching the briefing) is something that, as a game programmer, I'd definitely consider a bug.