The best part about WAR and the new saber-stats is that the math geeks have done all the heavy lifting. We get to use the fruits of their labors. WAR is an abstraction about baseball. It's not perfect and should not be relied on as the only measure of a player's value. More than anything it is a way to cluster similar players. Here's the graphic I posted yesterday:
In recent Giants history, the best season by WAR was Buster's MVP campaign in 2012. FanGraphs gives him 10.