This is probably one of the best Animes of the 2011 autumn season and has potential to become one of the best animes of 2012 provided that the second half of the series as is as good as the first.
Another thing that I like about Fate/Zero is how it builds up the plot from scratch although its part of the Fate Stay/Night and type-moon franchise. So people who haven't seen stay/night or type-moon will not necessarily lose out in understanding the plot and the characters (After all it is a prequel).