Is there any joy at Passover
Yalkut Shimoni, Emor, 23
One can find three kinds of joy written about a festival [in Succot]: “you are happy with your festival”, “and you were very happy” and “you were happy before the Lord your G-d for seven days”. However at Passover you cannot find one mention of joy. Why? Because at Passover the crops are discussed and no man knows whether he will have crops this year or not. And you can find that on Shavuot (Pentecost) only one joy is written: “And you made the festival of Shavuot to the Lord our G-d....and you were happy....you and your son and the gentile”. And why is that? Because the crops are brought inside. And for what reason it is not written that there are two joys? Because the fruit and the trees are discussed; however on Succot (Tabernacles), when the crops and the fruit and the trees are brought inside, there it is written three kinds of joy.
One thing [why do you not find in Passover even one joy?): Because the Egyptians died. And that you find: that on all the seven days of the festival we read the prayer of Hallel. However on Passover we only read Hallel on the first day of the festival and its night. Why? “When your enemies fall you shall not be joyous and when they fail you shall not put your heart aside.”