By the power of truth, I, while living, have conquered the universe.
Posted by: About 9 Grunts
No, military RPGs don't work well. RPGs are best when it's free roam, don't take orders from anyone but yourself, and have complete control over what happens.
It wouldn't have to be a military RPG.
In my eyes, a Halo RPG could work beautifully if done in a similar style to Mass Effect. Say you start with your protagonist, a Sangheili from long before the Human-Covenant war. You'd start out akin to the Dalish from Dragon Age: Origins, you discover some ancient piece of Forerunner (Eluvian) technology which draws you to the Covenant, as you progress you get a ship and a crew, you get to access a galaxy map to explore various locations in search of Forerunner relics.
If done correctly, it could be a fantastic hypothetical game.
EDIT: Or an Elder Scrolls/Mass Effect style Forerunner RPG would be just as amazing. Plenty of opportunities for the plot to go many places and some absolutely amazing environments (the Capital!) could be implemented.
[Edited on 08.05.2011 4:09 PM PDT]