The Easter Vigil is the way that the Church truly shows that Easter is the Sunday of Sundays - the greatest of all feasts. It is when we celebrate Jesus rising from the dead - destroying death and restoring us to eternal life. Yet, Easter would not have happened without Good Friday, which is why going to all the Triduum Masses allows us to fully appreciate the Resurrection.
There are several reasons why the Easter Vigil is much longer than an ordinary Mass. The Easter Vigil starts with the Service of Light, where we light the first fire, the priest blesses the fire, and uses the fire to light the Easter Candle. The light from the Easter Candle is used to light candles held by the assembly. As the entire church is in darkness, the lights from these candles light up the entire church, as the priest, deacon, or cantor sings the Exultet.
After this, all candles except the Easter candle are extinguished, and we begin the Liturgy of the Word. The Liturgy of the Word is also longer on the Easter Vigil, as there are anywhere from 2 to 7 readings from the Old Testament. After the readings from the Old Testament are read, the Church rises for the great Gloria (which had been put away for Lent, having only being sung on the feasts of the Annunciation, St. Joseph, and the Mass of the Lord’s Supper (Holy Thursday)), accompanied by bells. This is followed by a reading from the Letter of St. Paul to the Romans. Finally, the great Alleluia is sung, and the deacon (or priest, if no deacon is present) reads the Gospel.
After the homily, we go to the Sacraments of Initiation. The priest uses the Easter Candle to bless the new water in the baptismal font. He asks the Elect to renounce their sins and profess their Christian faith. The Elect are then led to the font as the assembly sings the Litany of Saints. The Elect are then baptized and leave temporarily while they change into their baptismal garments. During this time, the rest of the assembly is asked to renew their baptismal promises and are either sprinkled with or asked to bless themselves with the newly blessed water. After this, the neophytes are welcomed into the Church as newly baptized Christians, and asked to keep their baptismal garments unstained. Then, the neophytes are given the sacrament of Confirmation. In general, the sacrament of Confirmation is to be done by the bishop, but for the Easter Vigil, most bishops grant their pastors the authority to confirm in their name. The Sacrament of Confirmation consists of the laying on of hands and of the anointing with Sacred Chrism (the bishop/priest says “be sealed with the gift of the Holy Spirit” as he anoints with the Chrism). After this, the Mass continues with the Prayers of the Faithful, and then continues as normal.
As such, the Easter Vigil is much longer due to the Service of Light, extra readings, and the Sacraments of Initiation. Depending on how many readings are read, the length of the homily, and how many people are being received into the Church, the Easter Vigil can last anywhere from 1 1/2 hours to over 4 or 5 hours. In the early Church, the Vigil started at sundown and generally lasted until sunrise.