This is just the nature of urban warfare against an terrorist group that is deeply embedded in the civilian population. The tunnels add a huge level of complexity to it.

Israel did themselves no favors by projecting a message early on that they would be able to "destroy" Hamas entirely in a very short amount of time. It was probably inevitable from the beginning that this would be a long, drawn out conflict. Hamas will continue to exist to some extent for quite some time. But the fact remains that their military capabilities are far diminished now, and continue to be futher diminished. That is the essential goal of the war.