The story was disappointing, but only because I wanted more answers instead of the 'to be continued' line we got.
I think that the Locust was created by scientists. The COG, a socialist political party wanting human unity during the Pendulum Wars, may have created the Locust as a way to unite humanity. However, the Locust, who were suppose to be a weak and easily defeated foe, and most likely use to be human, ended up being a very strong enemy who is seeking revenge on humans who created them and drove them underground.
In regards to the sinking of Jacinto, I think that was a bad idea that will only hurt the humans in the future. After the death of the giant rock worm, the COG may have been tricked to sink Jacinto by the Queen, the Queen wanting to take out both the last human stronghold and the Lambent who are fighting the Locust as well. Dont be suprised if the Locust had already moved their headquarters elsewhere and humanity is on the brink of destruction in Gears of War 3.
Also, the COG president and the Locust Queen probably worked with each other on the 'Locust scientific project' and ended up betraying each other.
