All weapons used in a densely populated area are terrible. However, some weapons are forbidden under humanitarian law.
During the Gaza war 2009 there were rumours about Israel using cluster munitions, white phosphor and DIME. See e.g. Independend. So far only the use of white phosphor is proven. Israel claims all used weapons are legal. Please find some comments by experts. See a Channel4 documentary on transfer of cluster weapons and DIME through American military Airport in the UK.
On cluster munitions, a statement by the Cluster Munition Coalition.
On the use of white phosphor, Human Right Watch Q&A on White phospor and International Law and CBS news item from Gaza.
On DIME, a press article quoting two Norwegian doctors.