Q does have a point. Pretty much every sequel in pretty much every game series of note has had the same basic gameplay.
As far as game mechanics go, after GTA III, GTA's biggest changes have been common sense stuff that any series should do as technology advances. It wasn't particularly innovative to add flying vehicles and a 360 degree camera for firing a gun from your car, it was just the next logical step up. Assassin's Creed has made basic climbing and combat upgrades, but it's one of the most repetitive game series I've played, and it's amazingly successful. They're popular because of the story and graphical upgrades, and a gameplay formula that remains fun despite having few changes.
Infamous has always had a fun, interesting, comic book-style story. It just took them until the third game to make a real graphical upgrade, and the gameplay has made all the upgrades that were needed.
Also, the settings for the Infamous games aren't any more empty than Assassin's Creed's settings. The people are just kind enough to not get in your way when you're at ground level, or when there's a huge battle of flames and sparks and explosions going on.