The fight is going on. ISIL is starting disruptive tactics in Baghdad similar to the one used in Kabul ( car bombs, terrorist attacks).
It actually looks very organized as it is opening multiple fronts to stretch the Iraq Army response.
They reached the southern district of Baghdad in heavy numbers. This is important as it cut off reinforcement from the South, were the main army is and it cannot be attacked by airplanes without causing heavy civilian casualties.
it is spreading towards south. That is an extremely important piece of information as 70% of Iraq oil fields are in South Iraq. Saudi Arabia does not have enough spare capacity to calm down the oil prices at the moment.
ISILis likely to supplant Al Qaeda in your terrorist nightmares as it has a clear organization (funnily enough it even publishes an end of year report similar to what the listed companies do) and with this attack it also got hold of over US$420 million dollar in Mosul and probably more.
So practically ISIL is a terrorist organization acting with the sophistication of a well trained army – fast deploying unit and terrorist sleeper cell. And with Syria attacking with Baghdad blessing inside Iraq (and Iran shelling rebels positions inside Iraq) the Middle East situation can really spiral easily out of control – ISIL war is already spanning from Lebanon to Iran, with Jordan in high danger as there are not any more divisions between ISIL in Iraq and Jordan.