From The Birth of Tragedy:
Christianity was from the beginning, essentially and fundamentally, life’s nausea and disgust with life, merely concealed behind, masked by, dressed up as, faith in “another” or “better” life.
I think it bears noting that, while Nietzsche was indeed distressed by the lack of meaning apparent in a world in which God was becoming less relevant, he nevertheless found such a world necessary and desirable, because he believed that religion, and Christianity in particular, was a sickness in the world. He describes religion as the elaborations of a slave morality, which had been invented by slave classes throughout history to give meaning to their suffering and justify their weakness in their failing to rise up against their masters (I don’t agree with him on this, by the way). It was religion that he saw as nihilistic, forsaking belief in the true and immediate reality in favor of a future post-mortem unreality. And he saw the world as indeed lacking inherent meaning, subject to eternal repetitions without any progress or change. He despaired of this, as you say, but nevertheless found its truth unavoidable. Nietzsche’s aim in this was for people to joyfully seek meaning in a world that intrinsically lacks any, but to do so through art and philosophy and impassioned living.