I think 343 should consider making a Halo role playing game. I like the way you can change your armor in Halo 4 for diffrent stats and I thought to my self, this would be a awesome RPG... The story wont be around master chief but around a Rookie trying to go up in ranks.. Would have dungeons/quests and diffrent armor sets/classes, that would be a awesome idea.
Then yeah you have alot of options. Your probably aware of mass effect. Fallout isn't terrible. I could probably find a few more on steam. I know they're not the same base 100% concept you have in mind but its as close as your going to get.
To be honest from personal experience firefall is the closest you probably will get unless somebody can think of something different.