They wanted to avoid a universe where humans are good and orcs are bad.
Metzen wants to share the story of Warcraft with everyone, even those who don't play games--he wants to take the idea far and wide. Film is the ultimate storytelling medium (only rivaled by games!) so the Warcraft universe should be conveyed in this medium.
There are Easter Eggs for hardcore fans, but the movie is for everyone. For a non-gamer, they'll enjoy the lush world, for an avid WoW fan, you'll notice all the rich intricate details. Duncan Jones worked with Blizzard artists to get all the little details right.
The actors then introduced themselves and spoke a little about their characters. Ben Foster hinted that his character was isolated, but was told not to say more! Paula Patton LOVED talking about Garona. She was talking about how the script read like a novel, that her ancestry was fascinating. She spent most of her life as a slave, had to work to get respect among Orcs, and is now a fish out of water among humans. She found working on the movie a challenge and scary. The film to her is entertainment but also a mirror of the world we live in, with people fighting to protect what they love, people in power doing what it takes to make things happen, and people mismanaging power who turn corrupt.
Duncan Jones and Chris Metzen talked a bit about the challenge of adapting a video game, since WoW is an extension of players, it's your persona. They talked about how seriously they were taking it, how they have a huge responsibility to the players. There's a strong theme of family and loyalty when you play with your friends, which is mirrored in the film.
There was also a Q&A, here's the highlights:
Durotan lives in the moment, his life right now is about his land that's dying and becoming a father.
The actors only saw the finished effects for orcs several weeks into filming--it was a relief to see they weren't cartoons!
Gul'dan has unusual posture - had to be squatting hunched over throughout the shoot.
How true is the film to the story The film tells the story of the game Warcraft 1, which was later revisited in the novel The Last Guardian. However, it started in 1994 so the storytelling is a bit crude by today's standards. As time goes on, Metzen talked about refining the mythology and they did simplify and tweak the story a bit to make it work as a film. He still loves Warcraft 1 as a game but it's over 20 years old. So, fans should view the movie as an ultimate version of Warcraft 1.