The X720 & PS4 will be more powerful than the Wii U that is a FACT, both Sony & Xbox will make sure of this, the question is what will the developers do with the power.
For sure the 720 n ps4 will be more powerful they'd be mad not to be! and Devs will do what they always do with new powerful tech, make games that are bigger shinier spanglier faster...erm..stronger( eh? - the voice in my head) maybe not all that different gameplay wise from what we got now to begin with (depending on what sort of controllers etc the ps4 n 720 have of course) but a couple of years down the line they'll give us stuff that makes you go "oooh different".