So often we think of God as non-enthusiastic or even gloomy. The exact opposite is true: He loves to be God, He takes great pleasure in all that He does, and He is enthusiastic about serving His people and working for their welfare. For example, God says in Jeremiah 32:41: "I will rejoice in doing them good." Jesus said in John 15:11, "These things I have spoken to you, that my joy may be in you." And Paul writes in 1 Timothy 1:11 of "the glorious gospel of the blessed God." Blessed means happy. So Paul is saying: "the glorious gospel of the happy God."
God is infinitely happy because he is infinitely glorious. And, the good news is that he invites us to enter into his happiness. Here is what Piper writes in The Pleasures of God (p. 26): "It is good news that God is gloriously happy. No one would want to spend eternity with an unhappy God. If God is unhappy then the goal of the gospel is not a happy goal, and that means it would be no gospel at all. But, in fact, Jesus invites us to spend eternity with a happy God when he says, ‘Enter into the joy of your master' (Matthew 25:23). Jesus lived and died that his joy-God's joy-might be in us and our joy might be full (John 15:11; 17:13). Therefore the gospel is ‘the gospel of the glory of the happy God.'"