God is allowed to kill his own creations.
He does anyway, of course—natural death is part of God's plan just as much as violent death. In the end, God kills every living thing on earth.
If God really commanded the Israelites to kill certain people, that is not murder, because it was primarily God who killed those people, using the Israelites as his instrument.
A few years passed, and God killed every one of those Israelites, too.
So my first point is: Old Testament massacres are not any more of an argument against a good God than death in general is. If you can believe in a God who allows his creatures to die, you can believe in a God who commanded killings at certain specific times and places.
Next point: for humans, this life is not the end. It shouldn't need mentioning, but it does.
You hope for eternal life in this world because you don't believe in eternal life after death.
Well, guess what: God believes in eternal life after death.
To bring a beloved son out of this corrupt world and into a perfect one where he can reside happily with you for all eternity is an act of love, not evil.
The biggest problem with your worldview is a utilitarian emphasis on satisfying desires.
Desires do not contain any inherent moral imperative that they be satisfied. You can know that this is the case because desires are often contradictory. If contradictory desires both morally required you to satisfy them, then it would be impossible for you to behave morally well, which is a contradiction in terms.
Your desires are arranged in a hierarchy. The only desire that creates a demand upon your will is the single highest desire that you have. This is because it virtually contains every lower desire.
Suppose I could give you any one thing at all. Anything. What should you ask for?
An idiot would choose some finite good, like a harem full of virgins.
A slightly smarter person would ask for a reliable means of obtaining other goods, like a hundred billion dollars.
An even smarter person would ask for a means of obtaining the reliable means of obtaining other goods, say, to become able to learn and memorize any subject of study with ease, or to become irresistably charismatic.
Notice how we've moved here: the low physical good at first, then the high physical "means" to low physical goods, then higher mental/personality/spiritual qualities which allow you to make gobs of money at will.
But beyond that, you could ask for the wisdom to know what goodness IS. To know what exactly it is, that all of these lesser "goods" have in common, so that they are all accurately termed "goods".
And even beyond THAT…
You could ask to possess GOODNESS ITSELF, and contemplate it face to face.
I assert that this is, in fact, your REAL highest desire: to possess goodness itself.
In other words, this is the ONE desire you have which actually creates a moral imperative for you. It is the one desire you can never change, and it is the one desire which can never contradict any of the others.
I am here to tell you that GOD IS GOODNESS ITSELF, and that the promise of HEAVEN is precisely the promise of obtaining this, the highest object of desire in every human heart, which contains and subordinates every lower object of desire.
And this God has loved men so much that he has come down from heaven to earth, in flesh and blood, and showed us the Way to come into eternal life with him. His name is Jesus Christ.
He proved that what he said was true by rising from the dead.
Set down your pride already. It's a heavier burden than you think. Throw it out, and you'll feel light in a way you've probably forgotten that it was possible to feel.
Quiz:
Jesus said (Matthew 11:29), "Take my yoke upon you and learn from me, for I am…" (fill in the blank)
What's the answer?
1. …wise as a serpent, yet gentle as a dove.
2. …the Alpha and the Omega, the first and the last.
3. …the Way, the Truth and the Life.
4. …meek and humble of heart, and you will find rest for your souls.
So. Why should we learn from Jesus? What's the reasoning that Jesus gives? I'll leave it to you.