1. Because it is a remarkably stripped-down and spare piece of cinema, with no sex, violence, or swearing (because, assumedly, the filmmakers want people of all ages to be able to see it, considering their topic important); because it is further filmed with great craft and period accuracy in black and white; in other words, because it's an extremely rare and unusual phenomenon in recent American cinema.
2. Because it tackles an extremely significant period in American history (the McCarthy "witch hunts" of the 1950s) at a time when the moral questions raised need badly to be raised -- questions of journalistic integrity and honesty in the face of political injustices, questions of what it means to be a courageous and responsible member of the media when corporations and politicians would seek obeisance and silence on important issues. It directly addresses every journalist, every politician, every media figure in America and shows them by example what it is to be brave and honest and to do things that matter.
3. Because it is amazing proof that it is in actors that American cinema's greatest hopes lie; as with Sean Penn before him, George Clooney is using his own name and star power to make films that could not be made by anything other than a name star in America today, taking risks that few other people could take, using his celebrity to advance the cause of art, of moral cinema, of human integrity; John Cassavetes would be proud to see his legacy (tho' Clooney's filmmaking owes nothing in particular to Cassavetes).
4. Because it confirms that David Strathairn is the best working actor in America today (and has generally fine performances by the rest of its cast, tho' it's Strathairn that one cannot stop watching)... I love to see Strathairn get big roles; he's acted so well in so many independent films -- mostly those of John Sayles, of course -- that it's great to see him get recognition and money, and this is a meaty role indeed for him.
5. Because the clarity and eloquence of the language, and the force and even beauty of the arguments issued by its characters -- primarily Edward R. Murrow, as played by Strathairn -- is a delight; it is a rare thing to revel in the beauty of the words spoken by characters in a contemporary American film -- or to see any more-or-less mainstream film that really respects elocution to this degree.
6. Because it generates an amazing amount of dramatic tension using the most minimal of means and hits its mark with both grace and force.
I could probably squeeze out a few more but I'm tired and I think I have a cold coming on... It's a good film, though!