Excluding the forthcoming Halo Wars, once you start making Halo spin-offs, including if Bungie starts to make Halo 4, 5, or then 6, it will start to DEVALUE the Halo Trilogy.  Aren't endings supposed to include a little speculation?  That's what makes good endings good.  For the readers or gamers to think and dream of an appropriate ending is a GOOD thing.  Halo 3 ended the story, but left a little window for speculation, good job Bungie for a nice ending.

---

I don't want to kill you, it's just that you're too ugly to let live!

-Sergeant Johnson