1. The Warsaw Ghetto was designed to lock Jews in. In October of 1940 the Germans ordered the Jews of Warsaw to build (at their own expense) a walled off and barb-wired section of the city. Anyone attempting to leave could be shot on sight. Gaza has no such features as Gazans regularly come to Israel for medical treatment. Israel never required them to live there and would not protest if a Gazan desired to emigrate.
2. The Jews of the Ghetto lived on a starvation diet. The average daily amount of calories consumed in the ghetto was 184. Consequently, many Jews, including many children, died of starvation. Gaza, on the other hand, receives thousands of tons of food and medical supplies from Israel itself through the Kerem Shalom crossing - even in wartime. No one is starving.
3. The Warsaw Ghetto received no international aid. The Jews of Warsaw were on their own - which is why most of them died. Gaza, however, is the recipient of extremely generous amounts of money. In 2013, the US alone allocated 440 million. Sadly, much of this assistance seems to have been used to buy rockets and build terror infrastructure.
4. The Warsaw Ghetto was ultimately a way station to the extermination camps. An estimated 300,000 out of a total population of 400,000 were either gassed in Treblinka, died in the ghetto uprising or died of starvation. While the Jews were actual victims of genocide, there is (quite obviously) no such plan for Gaza. In fact, if the Israelis are attempting genocide on the Palestinian population they are doing a very poor job as their population has actually increased by 2 million in the last 20 years.
5. The Jews in the Warsaw Ghetto had no state sponsor of weaponry. They were able to fashion some simple incendiary devices and smuggled in some guns and bombs which they used to stage their well known uprising in 1943. The Hamas rulers in Gaza receive thousands of short and long range rockets, automatic riffles, anti-tank rockets and mortars supplied by the Iranians. Many of their fighters have undergone advanced military training. In short, Gaza has a professional army - one that the Jews in Warsaw lacked.
6. The Jews in the Ghetto had no diplomatic backing. There was no UN or EU or Arab League to stand up for them and decry their inhumane treatment. The Gazans have the ardent backing of each of these organizations and many others and are able to parlay world sympathies into leverage for more favorable cease-fire agreements, increased funding and as a tool to harm Israel's international standing.
7. The Jews in Poland didn't do anything to the Germans or Poles. Polish Jews had been quiet and productive members of Polish society for 1000 years. Hamas, by contrast, was founded in 1987 for the express purpose of killing Jews as is stated in their charter in 12 places. So whereas there was no logic to keeping the Jews separate from the Polish population, there is excellent reason for the Israelis to maintain strong and high fences between themselves and Hamas.
8. When the Germans attacked the Ghetto, they systematically annihilated it block by block until nothing was left standing. When the Israelis counter-attack Gaza they do it though an unprecedented series of warnings via leaflets, phone calls, text messages and the like. So while the Germans did everything they could to raze every building, the IDF exerts the same type of effort to preserve them.
In short, Gaza is nothing like the Warsaw Ghetto.