Honestly, I'd be like Lelouche in a sense, if it were me. I'd use it to my own ends, probably create a huge amount of chaos, and get my own way. All those things I'd do would be a one-way trip to hell, easily. It all depends on WHO gets that power, as It's been stated the Geass manifestation changes from person to person. Ie: Lelouche absolute obeying, Mao hearing thought 500 meters outwards, etc.
Not every person would get Lelouche's.