It's safe to say the folks making Sunset Overdrive never intended to make a serious shooter. I mean, setting your game in a world where a tainted energy drink turns people into mutants (that you can then dispatch with a firework-launching flare gun) doesn't exactly suggest "gritty." They even poke fun at the overwhelming number of realistic cover-based shooters in their E3 trailer.
Which you should check out.
Looks like someone was playing Dead Rising and thought "You know what I miss. Tony Hawk."
Imagine seeing eight players grinding on rails and blasting mutants into orange goo all at the same time. You might lose your mind, or straight up vomit rainbows and punk rock.
Source: Xbox.com