HBO's big-budget take on one of my favorite books, "A Game of Thrones" by George R.R. Martin, is finally marching across America with an invasion of advertising. Posters began going up this week in cities like New York and HBO has released several trailers for the series, which launches April 17. Check out the preview called "Fear and Blood." The epic visuals and obvious investment behind the show come as a great relief to die-hard fans of Martin, an often-underappreciated author known (accurately) as "America's Tolkien."