Well, for one.
It's even more over the top than part three.
In IV, you're the president who has to fight against some sort of alien invasion.
You also get superpowers.

It looks really fun and I'll probably buy it because I do sometimes enjoy playing games that go way over the top and gives me a laugh.

Though this is totally different from how Saints Row used to be, I am pretty excited but neutral about whether this is good or not.
From gang warfare to being a celebrity to being a president with superpowers? I don't know if that will work out.

http://www.youtube.com/watch?v=8LYfCs5bfyI