Besides being translated from the Greek εὐαγγέλιον (euaggelion), the Gospel is Good News because it answers the Bad News, as demonstrated in Ephesians 2:1-10:
H – Human Depravity – “And you who were dead in trespasses and sins” (2:1)
O – Original Sin – “Wherein in time past ye walked according to the course of this world, according to the prince of the power of the air, the spirit that now works in the children of disobedience: Among whom also we all had our conversation in times past in the lusts of our flesh, fulfilling the desires of the flesh and of the mind.” (2:2,3)
W – Wrath of God against sin – “…and were by nature the children of wrath.” (2:3)
God’s answer to this is The Good News.
”But God, who is rich in mercy, for his great love wherewith he loved us, Even when we were dead in sins, hath quickened us together with Christ, (by grace ye are saved;) And hath raised us up together, and made us sit together in heavenly places in Christ Jesus: That in the ages to come he might shew the exceeding riches of his grace in his kindness toward us through Christ Jesus. For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast. For we are his workmanship, created in Christ Jesus unto good works, which God hath before ordained that we should walk in them.” – Eph. 2:4-10