This one's tough to answer, not because the PS4 isn't expected to be superior because it's obviously the more powerful hardware, but because the question isn't "IF", but "How Much".
1) As some have already pointed out, the PS4 not only has the brute force power but it's also the easiest architecture, this gives the PS4 an advantage for un-optimized code which is what you get at launch since games were being built on a moving target.
2) Most games this gen were built with the 360 as the lead, this gave 360 an advantage with multiplats. This upcoming gen things are changing. With PC gaming gaining lots of traction, most multiplats are now being built for the high end PC, then ported down to consoles. Watch Dogs, Battlefield 4, Assassins Creed 4... you name it, these games will perform best and will look best on the PC, then the consoles will do their best to replicate the original.
Now here's the tough one, how faithful will PS4 and Xbox One replicate the PC versions of these superior games? I think this gen right out the bat we're going to get a clear answer of what the difference in power translates to. The PC will show us what these games are supposed to look like, while the consoles will do their best to replicate them. Head to heads will have a lot more meaning this time when comparing PS4 and XBO games, and one could say XBO has a bigger learning curve, well sorry but that's part of the equation, if your console is harder to take full advantage, then tough.