"This is a faithful saying: For if we died with Him, We shall also live with Him. If we endure, We shall also reign with Him. If we deny Him, He also will deny us. If we are faithless, He remains faithful; He cannot deny Himself." (2 Timothy 2:11-13, NKJV)
Good Friday is of course the day that many commemorate the death of Jesus on the cross. He paid the sin penalty of all those who through faith died with Him. Good Friday is good not only because Jesus paid the penalty but He triumphed over sin on Sunday.
This Sunday is called Easter Sunday. A better term would be Resurrection Sunday. The resurrection of Christ is the central element to Christianity. The church has a tendency to focus more on the cross than on the resurrection. The cross is an essential part of our redemption, but if Christ did not rise from the dead on Sunday then the cross would be a meaningless act.
"And if Christ is not risen, your faith is futile; you are still in your sins!" (1 Corinthians 15:17, NKJV)
Good Friday is good because Jesus has risen from the dead!