Both Hamas and Israel spent over a year preparing for the ground war they are currently involved in. Hamas based its tactics on those use by Hezbollah during 2006, which the Israelis refined the techniques that had proved successful against Palestinians in the past, and built a new training center, and infantry training program, that several brigades of troops have gone through. These are the troops now in Gaza, or headed there.
The Hamas tactics are not exactly like those used by Hezbollah, because the battleground is different (built up areas, not the open country of southern Lebanon). Moreover, while most civilians fled southern Lebanon before the ground fighting got to them, the civilians in Gaza have nowhere to go. Unlike Hezbollah, Hamas seeks to get as many Palestinian civilians killed (by Israelis, preferably) as possible, so they can claim to be the victims of an Israeli genocide, and cause a sufficiently powerful diplomatic response from the West to force a ceasefire. Otherwise, the Israelis will capture or kill most of the key Hamas personnel.
Hamas also hasn't got the weapons Hezbollah had. In particular, Hamas has not got the Kornet E, a Russian laser guided missile with a range of 5,000 meters. The launcher has a thermal sight for use at night or in fog. The missile's warhead can penetrate 1200 mm of armor, which means that the side armor of the Israeli Merkava tank would be vulnerable. The missile weighs 18 pounds and the launcher 42 pounds. The system was introduced in 1994 and had been sold to Syria (who apparently passed them on to Hezbollah). Hamas may have gotten some Kornet (or similar) missiles, but none have shown up yet. The Kornet was used to best effect against buildings Israeli troops were in. With assault rifles and RPGs (the primary weapons of Hamas) Hezbollah was not very effective against the Israeli infantry.
Israeli intelligence had already figured out most of the Hamas war plan, aided by anti-Hamas Arabs in Gaza, and other forms of surveillance. Once inside Gaza, Israeli troops quickly captured more documents detailing Hamas tactics in general, and specifically (for particular villages). Hamas was making much use of bombs (booby traps and command detonated ones). Some of the bombs, like those in gasoline stations near residential areas, were meant to cause lots of civilian casualties. Hamas also set traps that they hoped would result in the capture of Israeli soldiers. In contrast, the new Israeli infantry tactics were specifically designed to avoid that, as well as avoiding the booby traps and Palestinian civilian casualties.
Israel has kept all reporters away from its troops, and Gaza territory it controls. Hamas has al Jazeera and reporters from a few other Arab media. These journalists swallow just about anything Hamas feeds them anyway, so the Israelis don't worry about it. Inside Israel, there is wide support for the war in Gaza, and the Israelis appear determined to stay in Gaza until they have captured or killed all the key Hamas personnel, and destroyed the thousands of rockets Hamas is believed to have stockpiled. Some of those rockets are still being fired into Israel. But the number has averaged 30-35 a day, and it's been declining since ground operations began.
Hamas also has to worry about enemies within Gaza. Hamas gained power in Gaza through violence. Hamas also used more violence against its enemies than is customary in Palestinian politics. This created some deep animosities in Gaza, and a lot of Gazans are eager to see Hamas fail, and suffer a lot on the way down. Israeli troops know that they have done more damage to Hamas, than Hamas expected. Electronic eavesdropping, captured documents and captured personnel all tell the same sad, shocked story. But Hamas is an organization of religious fanatics, and nothing encourages this kind of personality like the prospect of imminent destruction. The next few weeks will be full of violence and surprises, but Hamas winning won't be one of them.