Just thought I should add, the gameplay trailer is pre-Alpha because obviously, marketing has to plan very far ahead (in terms of strategy blah blah blah) to get the game the most attention and boost sales. So this trailer would have been made before they reached the Alpha stage, as it takes a long time to be created, edited, and then released properly. It's impractical for them to create a trailer from an alpha build and release it within a few weeks.
So basically, it takes months to release a trailer. Expect Alpha build at E3.