Frankly, Matthew McConaughey would be an excellent Tom Joad. But I'm not sure that what you were expecting from Christopher Nolan was a movie focusing quite so much on McConaughey reiterating how much he loves his kids, while the Earth has a harsh summer.
Nolan has enough control over his stuff that I'm hoping - hoping - this is all first-act stuff because he doesn't want to spoil things. Because if this were a trailer for any other movie by a less-known director, it'd be giving me Contact vibes, where, to quote South Park's Mr. Garrison, you wait the whole movie to see the alien and it turns out to be her goddamn father (this is making me think aliens will manifest as his kids). If that's still a spoiler to you all this years later, I've saved you some time.