re: Halo Anniversary - they have mentioned it being a less than full price game, but they did plan the same for ODST initially so Fingers crossed.

Apparently there's some event in August where they'll reveal more on Halo 4 and let people get their hands on halo anniversary.

It's been a certainty for a while now that there'd be more halo games and why not? - they make money. 343 Industries was set up specifically to handle HALO releases.

Halo 3 was also open ended with somewhat of a cliffhanger.