Don't miss the setting of Psalm 88 near the end of the alternating pattern of psalms of communal laments expressing the people's abandonment by God, followed by psalms of hope in God's faithfulness, that runs through Book 3 of the psalter. Psalm 88 is the darkest lament, followed by Psalm 89 in which it looks as if the covenant God made with David has been renounced because of the people's unfaithfulness which resulted in the Babylonian exile. Where is hope to be found in such darkness for Israel? Psalm 90, the beginning of Book 4, points Israel back to Moses, reminding them that God had been faithful to his people through a comprehensive judgment upon their faithlessness before. So too there was hope for Israel in the God who brought them out of Egypt and through the Wilderness (key themes in Book 4). From Psalm 90 onward, the predominance of laments in the psalms is replaced by a predominance of praise, centering on the reign of the Lord over all.
So Psalm 88 speaks of Christ as the new Israel, experiencing the undeserved judgment for their sins in its fullest depths, in whom is their (and our) only hope. It also speaks a word of hope to us when we find ourselves in the depths, reminding us that we are united to Christ in his sufferings that we might also be made like him in glory.
(For a persuasive explanation of the message of the psalter as a whole, I highly recommend O. Palmer Robertson's book, The Flow of the Psalms).