They had huge press in Iraq when they convoyed up from Baghdad and Samarra with flags flying and everyone twitting and posting. They attacked on 2 March, and got bogged down into a high casualty stalemate. There has been a lot of press about them pulling back for the Americans to show them how its done.
Here is Internet media hog, Abu Azrael, who posts online as frequently as a Kardashian:
He has been a big inspiration to the popular mobilization units (militias), and the Shia public.
The Iraqi Army and paramilitary Federal Police have a few thousand each - but much better armed and trained - supported with very heavy air attacks, including the bunker busters which can defeat the fortress-like old palaces of Saddam, where ISIS has been safe until now. All the regular Army guys need to do is identify ISIS positions and call them in, then report how well they blew up. They can wait until the door is blown open and unguarded before advancing.
Three nights will be pretty good, but a week of this will be very good for them. It is dawn in Tikrit now, after the fourth night. There were reports that the Army was probing more heavily on Saturday. The initial target sets have probably all been hit by now, so they are probably trying to provoke ISIS into firing, so they can see where to drop the next bomb.
ISIS is reported to have from 100 to 800 hundred survivors, but consensus seems to be more like 200-400, or even less. They are probably losing a few dozen per day, with injuries mounting and guys getting punchy from explosions nearby, lack of sleep, and seeing all the gore and death close in on them. No surprise what is coming for them - they are trapped.