I think going for a gruff badass soldier probably isn't the best move though. It's typical, but it also fails to differentiate a spin-off from everything else. It's easy to pigeon hole the mass market for loving these kinds of characters, because they do, but the failure of clone games indicates people are more attached to familiar franchises versus everything being the same.
BioShock's character was neither of those things, and Infinite's isn't either.
As far as MC go, I have wondered recently if the MC has to be a human. You could make a Metroid type game, and have the MC be some type of other life-form, to differentiate yourself from the "tough, save the world person" image that every game goes for now and days.
When I thought about it though it got me realizing how most big games, even ones that focus on other "creatures", the MC is almost always human, and it made wonder if that's important, or a coincidence. In games like, ME, GoW, Infamous, Bioshock, Halo, most FPS etc, the MC is almost always a human, and I was wondering is that because it gives the player some extra emotional attachment that is necessary, or would those games have done just as well with some sort of mascot MC?