With regard to the Old, the Book of Hebrews states that it was ready to disappear before the New (Heb.8:13). In his epistle to the Colossians, Paul mentions that Christians do not need to observe the feasts and festivals since their purpose is over (Col.2:16,17). The feasts were only shadows of the reality, that is Christ, to come. One doesn't need to go back again and again to the sign posts after having followed them, crossed them, and reached the destination. One doesn't keep gazing at a picture the whole day when the real person is close by.
Now, while some may choose to celebrate the feasts (which is not prohibited), one must not teach that the feasts need to be celebrated (as if it was mandatory), for that violates the Spirit of freedom, the New Man, and the Perfection of the New Covenant. We can look back to the feasts as having typical significance for Christ. However, observing them or not observing them doesn't make any difference to one's position in Christ. The Law can neither control us, nor curse us, nor condemn us.
Feasts of Israel
Feasts: Typical Significance
Three Purposes of Feasts
The Lord of the Sabbath