I appreciate all your suggestions, but I'm not really fond of any of them -- apart from Halo being taken away from 343 
I don't think a big budget and a better engine separate a poor game from a great one. Banjo-Kazooie and Tooie were great because of the brilliant minds at Rare at the time and the stewardship of Nintendo. Microsoft throwing money at Playtonic to make Threeie isn't the same thing.
I would love a new Conker, but who's going to make it?
I like the idea of Microsoft doubling or even tripling down on its bread-and-butter, shooters, but I don't trust 343 to make a new Perfect Dark.
Lost Odyssey 2 and more RPGs in general is a great idea. Bring back Fable; there isn't really anything like it on the market. I'm not wild about Halo RPG. I would like more RTS games in the style of Halo Wars.
A survival-horror game is a nice idea, but I'm unsure if the Gears milieu is the best place for it.
In general, I think you're right that Microsoft needs more shooters, more RPGs, more everything. I think it needs to do much more than bring in hired guns to handle an IP or ressurect an old property just because it's there. It needs to build up its internal studios, hire visionary talent, and form meaninful, long-lasting relationships with indie and Japanese developers. When Xbox was at its apogee it was getting amazing first-party-published games like Halo 3 and Reach, Gears of War 1, 2, and 3, Fable II, Ninja Gaiden II, Lost Odyssey, Mark of the Ninja, Shadow Complex, etc., plus all the high-profile third-party "AAA" games. It needs to do that again in order to compete with PlayStation.
