Shooting games (mw2, BO) are too common so I would take a different approach, Make it very realistic, not necessarily the graphics but don't have it like sonic the hedgehod.
I love westerns so if I was to make a game I would base it around Billie the Kid
My second choice would be something like Metal gear solid 2: Sons of liberity. My favourite game ever I used to play for hours and hours and never get bored soo yeah, Good luck keep us up to date on your progress