I suggest you read the Bible in its own context. The big issue in the Bible is how God is revealed as a God of justice and mercy – infinite justice and infinite mercy.
What you might be describing as bloodthirsty is not described as such in the Bible.
On its own terms, the Bible describes Jesus’ death as an atonement for sin. Now, you’re on to something deeply mysterious, in that 1) anything at all could atone for sin, and 2) that the death of Jesus, of all things, could atone for sin.
God is revealed in the Bible as infinite, “ineffable” – we can’t adequately describe the nature of God. But, one thing we believe is that he doesn’t need anything. So, he doesn’t need the death of Jesus, for anything.
Sacrifice in general, and the sacrifice of Jesus life in particular, are ways that God has revealed to us how much God loves us, that he would allow the sacrifice of Jesus on the cross. Jesus shows his love for us, that he was willing, in obedience to the Father, to give up his life for us on the cross.
Why?
One of our greatest gifts from God is our free will. When we use our free will to sin (to disobey God’s laws), we offend God. “offend” is the best word we can use to describe the effect of our sin on God – to use our free will to offend God.
We have only to look at Jesus’ suffering on the cross to see how much our sins offend God. They offend God to the greatest point that we can understand, somebody’s physical suffering from torture, and then death itself.
It’s a different subject, but a related one: the late Pope John Paul II said in a book called Crossing the Threshold of Hope, that many people do not believe in Christianity or cannot believe in Christianity, because they cannot understand how God has chosen to reveal himself and his will. So, perhaps this is why you cannot understand this, because it seems so improbable, to put it one way. But, this is precisely what has been revealed to us, and what we believe.
No, God is not bloodthirsty. In fact, somewhere the Bible says that God does not desire the condemnation of anybody, but rather would that each person would believe and be saved. And, that is the point, that belief requires us to use our free will to search for God and to worship him in love. THAT is the God that we believe in – a God who desires our love and devotion.