The gospel is the Good News that Jesus Christ came to earth in history, lived the perfect sinless life that we should have lived, and died a perfect sacrifice on the cross, all on our behalf, so that we might have life in his name. Jesus was dead and buried for three days, and then he was resurrected, and he ascended into heaven where he is with the Father, as an advocate before the Father for all who believe.
The gospel includes the biblical truth of the atonement (blood sacrifice, pointing back to the OT), which involves redemption of sinners who were enslaved to sin, propitiation of the wrath of God, and true justification because of what Jesus did for us on the cross. Romans 3:21-26 explains this and teaches that what Jesus did for us is a gift from God to be received by faith. Those who believe are justified before God, who is just and the justifier of the one who has faith in Christ Jesus.
The gospel would not be Good News if we had nothing to be saved from. But the Scriptures are clear that all have sinned, and all fall short of the glory of God (Rom. 3:23) and the wages of sin is death (Rom. 6:23). We were created to worship and obey God, but we have all turned in sin to idolatry and have rebelled against God. That is our fallen condition, which shows our great need for salvation.
It is also appropriate to add that, because of the depravity of sinners (including me), no man or woman will turn in saving faith to Christ without the Spirit first drawing them into the light. So, the gospel begins with theology, not anthropology.