I couldn't help myself and unlocked it early, and I've just completed the series of intro missions.
It's too early to say for the rest of the game, but so far everything is 200% of Saints Row 2. Like literally everything you can think of.
The most recognizable thing is the weapon mechanics which seem virtually the same, the AI is just as dumb as it was before, but responds with a bit more patos to getting shot. Most critically the vehicle handling seems a lot more responsive, but the cars are still fast as hell.
It's truly weird to start an open world game as a rich businessman, rather than say a balkan immigrant or a down on his luck loser with mob ties, but it's weird in the good way. Oddly enough the dialogue actually strikes me as pretty good. Everybody's very aware of being celebrities, and that's always abrasive, but they actually seem like friends when talking to one another. Actual friends, just talking, without some incessant need to convey information about who they are and what their relationships to one another is. Characters actually enjoying eachother's company, instead of serving up poorly hidden plot devices. How refreshing! Chris Nolan should definitely play this.
If I had to jump the gun, I'd say that for people who loved Saints Row 2, this is gonna be awesome, and for people who didn't, it's going to be just as bad, if not worse. It's an irreverent open world action game, that doesn't skimp on the irreverence, or the action.
It also manages to fuck with itself. The recap ends with the words "And Pierce.... Well, who gives a fuck about Pierce" - Who indeed. That guy is a goof.
It seems to me like another game that does everything GTA IV failed to do, while not trying to do any of the things that GTA IV actually did - of course including the neat stuff like the amazing tech and what have you.
So far though, so fun! The only negative is that the character creator seems to want to force you into metro sexual territory, but given the Saints new status, I guess that makes sense. Boohoo at that anyway.