Agreed. That concluding scene in 'The Composer' was quite a leap forward for the franchise. I expect, as the 'darkest Halo', and the fact that 343 are acknowledging how terrifying the Flood can be, we'll be seeing more mature content in Halo 5, and beyond. We could see scenes such as those depicted in the 'Mona Lisa' short, or Escalation - with the gathered souls, and 'Chief plunging his knife into the Didact's eye. There was a goofiness to Halo (aside from Reach) - which is fine, it was part of the appeal - that prevented it from really justifying the rating, but I think 343 is definitely more focused on telling a far more serious, and compelling, story in their games; which will justify that 'M'.