The developers of Prototype released Hulk already in 2005 (sandbox city game & super powers): 

http://www.gametrailers.com/video/cyclone-hulk-ultimate/7141?type=flv




That's the main inspiration for Infamous.

But Crackdown was publicly announced at E3 2005. And a lot of detailed gameplay of Crackdown was shown in 2006.

Crackdown was released in Feb 2007.

Then Infamous gets publicly revelead at E3 in June 2007 with just a short teaser trailer.

So Infamous was probably inspired by Crackdown as well.

inFamous is actually more like Ratchet and Clank, in an open world setting.

It has platforming and a more developed combat system than Crackdown and GTA.

Climbing buildings in videogames has also been around since Spiderman 2, and even earlier, if you include the arcade game Crazy Climber.  It doesn't mean it had an impact in console play and being done.

I mention Fable in here, because Fable held the PROMISE that your moral choices shaped the world.  I don't believe Fallout had that.  If it was just morals, then you go back to Ultima 4.  Balder's Gate also had this.  The aspect of moral choices shaping the game world in inFAMOUS, is why I bring it up.

Anyhow, the main point here is that, if someone happens to like their moral choices shaping the world, like Fable promises, then inFAMOUS would be of interest to them.