The console now has new monitors. A machine emits steam, and imagery is projected onto the steam to give it a really strange, interesting new look.
They added a set of stairs and a balcony to the set, with a door leading further into the TARDIS. This means they'll be able to do more scenes inside the TARDIS, not just at the console room.
They've re-jiggered the walling a little bit, moving a few of those hexagonal light panels and taking out one of the walls to give the TARDIS more space. This, as well as the balcony, will probably make the TARDIS easier to film in and allow for more dynamic shots.
There's a new crystal on the ceiling of the TARDIS to match the one in the middle.