I just finished the book last night. These viral videos are great. Scott did a good job with them leading to Prometheus too, despite the shortcomings of the film itself.
Kristin Wiig as Annie is perfect! She was probably my favorite secondary character, and I'm sure Wiig will pull her off well.
For some reason I doubted Matt Damon as Watney, until I saw these viral videos. I forgot about some of his guest appearance stuff that should have made me believe he could pull it off (like in House of Lies or Jimmy Kimmel stuff).
I've been avoiding anything at all related to this film until finishing the book (and still avoiding official trailers), but man they assembled a ridiculous cast! I get to see another film with Michael Pena in it this year?! Can't wait until he delivers one of the lines from the book. A little disappointed that Chiwetel Ejiofor is Venkat. He's a great actor, but the audio book narration did a great job making him a believable Indian character, that I felt like I had met before.
Man that cast is great though. Sean Bean as Mitch, Jeff Daniels as Teddy, Glover as Rich, Chastain as Lewis, and on.