The only thing I think that is milking the franchise is releasing the three old books. I don't want those changed just so Micro$oft gets more money, I mean so canon errors are fixed...
None of the games have milked the series so far. We had an epic TRILOGY (Halo Combat Evolved, Halo 2, Halo 3), so one could expect three games from that. We had a spin off (Halo Wars) which was done in a completely different style while staying true to the series we know and love. We had an expansion (Halo 3: ODST), which people should be happy for, but instead complain about. And now we are getting a new game in the series (Halo Reach) which follows the formula of the trilogy, and looks GREAT! so far.