As I commented here:
To them [the disciples], at that time, this [the cross] was disastrous. However, [Giles] Fraser is entirely wrong to suggest that the cross, “celebrated as a moment of triumph”, is “theologically illiterate”. He claims the end of the story does nothing to change this fact. However, the cross is a moment of triumph specifically because it is not the end of the story. Indeed, this is why Paul and the other apostles pinned their entire claim of Christian faith on the resurrection of Jesus Christ.
Rather than flesh out those details myself, why not read this and this.
So, what makes Good Friday good? The resurrection of Christ. What makes the resurrection of Christ of any value? The events of Good Friday. We cannot have one without the other.
The apostles rarely taught about the cross without mention of the resurrection. Worryingly, our gospel preaching often considers the cross whilst simultaneously ignoring the resurrection altogether. How often does the resurrection feature in your gospel preaching? Does the resurrection even make any difference to your gospel preaching? The apostles were clear that it should make all the difference in the world.