EncodedNybble on 29 March 2010
I say U2 because it's the most accessible of all of the options.
Most people like or at least can tolerate action games. Thus there will be a lot of people who wouldn't like Demon's Souls or KZ2.
GoW III is pretty violent and can be too much for lots of people.
MGS4 relies on a lot of previous story elements to reach it's potential (U2 does too somewhat but not as much). Also, stealth action and a lot of long cutscenes might be a turn off to some people.
So, I say U2 has the best balance of gameplay, looks and story that would appeal to the masses.
