If or when they enter Gaza that will alter if they dont reach their objectives hastily. I expect ambush after ambush from the maze of tunnels below them. Pop up in one spot to attack and disappear again to appear behind them. IED's and snipers galore and Hamas getting up so close to the Israeli infantry that the IDF air power is of no use. Artillery, tanks and other armoured support will be of little use because they require lots of infantry support in urban areas and manoeuvring in rubble filled streets is a major issue but that's providing that they use armour at all. Fighting in built up areas is heavily on the side of the defender and I expect the IDF casualties to be very high which inevitably leads to a loss of morale if you get bogged down. Then you have to hold the area you've captured and protect it from being infiltrated by hidden tunnels. It's a man power sponge. It's a safe bet to say Hamas has arms and ammo and has been planning their defence for a long time.