I had a chance to speak to the developers at the Eurogamer Expo. It will be very similar to the PS3 version except the graphics and framerate will be better. Expect it to look sharper and shiny with no performance issues. The current gen versions all suffer with performance issues but not enough to spoil the game.
If you are getting a PS4, then its worth spending the little extra to get the PS4 version.
ive had a go on both and theres not much difference the graphics only look slightly sharper but I see amazons put the price up its not worth the £15 extra difference from xbox360/ps3 versions the one which I think will be best is the wii u version if its anything like lego city undercover itll be superb
I can't remember where I read it but there was an interview with one of the people behind it and they said that there were more lego pieces, flashier special effects, no load times and includes support for the touch pad. So it sounds like it might be worth getting it for the PS4 instead of the Ps3.