Easter is not just "Easter Day," it is the fifty days from Easter Day until the Day of Pentecost. Easter is, so to speak, the "Sunday season". Every day of the Easter week is liturgically like a Sunday, and is of a similar rank as Easter. The following days are a further extension of Easter: the Sundays following Easter, often wrongly called "First Sunday after Easter," "Second Sunday after Easter," or (better) "Second Sunday of Eastertime" etc., are rightly called "Second Sunday of Easter", "Third Sunday of Easter" etc.
All the 7 weeks of Easter (a week of weeks) preserve an Easter and Sunday character. These fifty days, approximately a seventh of the year, make up a great "Sunday" in the yearly cycle.
The season of Easter has always been a time of joy and celebration. The Council of Nicaea, to favor this spirit of joy and celebration, even forbade fasting and kneeling during the fifty days of Easter.
This keeping of Easter as an extended celebration of the Resurrection has unfortunately been very much lost. I was struck today reading a pastoral letter of Bishop Conlon, of the diocese of Steubenville, inviting the Catholics of the diocese to resume the practice of abstaining from meat on Friday, and stating "The resumption of year-round abstinence in the Diocese of Steubenville will begin after this coming Easter, one week after Good Friday (April 17)." Of course this is certainly a good practice, but in fact, he chose the most inappropriate day possible to begin it. The Code of Canon Law, which in general preserves the law of abstinence on Fridays (though permitting the conferences of bishops to substitute other forms of penance), states that "abstinence from eating meat" is to be observed on Fridays unless they are solemnities. Easter Friday is a solemnity, indeed the greatest solemnity of the year that occurs on Friday. So this would not traditionally have been, nor according to the Code of Canon Law be a day of abstinence. The particular point about the starting date for beginning the practice is a small one, perhaps, but does seem to point to a certain regrettable lack of liturgical understanding.