It hasn't been milked nearly as much as Nintendo franchises, or Call of Duty. I don't see you can even consider them to be milking this franchise. They've only released three games in the main series, Reach being a fourth. ODST does not count, as it was more of an expansion to Halo 3. If releasing four games in a successful IP over the span of nine years is considered milking the franchise, then I'm going to eat my cat.
ODST certaintly counts-- although it WAS originally intended to be an expansion, they turned it into a full-fledged game, and it was sold at full price at retail. You're also forgetting Halo Wars.
And of course it hasn't been milked as much as Nintendo's franchises, nintendo has had 20 years with its main series', while halo has only been around since 2001 or so.
That said, I like the halo series, and I'll play the next one. The reach trailer was pretty uninteresting to me tho <_<