I think the strength of Islamic extremist militias like the Taliban or ISIS is the steady inflow of fresh fighters. They are very resistant against casualties inflicted on them, remember, the US military in Iraq (from 2003 to 2006) killed ~40.000, wounded ~200.000 and captured ~20.000 insurgents ! But they are still able to attract new fighters...
ISIS is also taking heavy casualties, especially when they try to fight like a conventional army (like in Kobane) and especially now with US warplanes in the sky.
Its not like they have a unlimited number of tanks, technicals or artillery. Every day they loose more and more equipment because of the airstrikes.
If you ask me, Kobane will be the last time they mass their combat power for a full scale assault. They may have enough human material but such heavy casualties dont fit with their propaganda.
US airpower will force them to fight a traditional guerilla warfare with a focus on defending their territory, terror (suicide) attacks and smaller assaults (hit and run).
About the Iraqi army performance:
http://warontherocks.com/2014/07/inside-the-collapse-of-the-iraqi-armys-2nd-division/