It is specifically there so that the Executive Branch can act without legislation. He can't do everything b/c it has to be constitutional (ultimately decided by courts) and when he needs actual funding, ultimately it comes down to Congress. But this Executive Order has nothing to do with something that Obama may have signed previously (which would have also had to go through Congress).
Most of his executive orders to date have been hand-waving BS, but this had actual real consequences on people day 1 and created a huge amount of confusion, not to mention whacking the hornets nest (what better way to help ISIS recruit) and not even addressing the main countries of concern (like Saudi Arabia).
The reason it is getting a lot of press and action is because it was incredibly stupid, reckless, and damaging.