This is by far my favorite book of all time for several reasons. Steinbeck always creates some of the deepest characters I've ever read. Tom Joad is my favorite character in any piece of literature. His growth from a self-serving ex-con to a Christ-like hero is an embodiment of the entire Joad family. Every time I read his lines to Ma when he says "Every time there is a cop beatin' a guy...look in their eyes Ma, You'll see me" or something like that, I think of that Rage Against the Machine song and I get chills.
Also, the way Steinbeck deals with immigration issues and poverty are great. Chapter 5 when the poor farmer confronts the tractor that is going to kick him off his land blows my mind every time. It deals with a time when the US economy was shifting from rural to urban in increasing numbers. It also is a clash between a farming economy and a capitalist economy with the captialists winning out. The description of the bank as a monster that must be fed for reasons we don't understand is very appropriate.
Steinbeck wrote an amazing book that I would anyone to read.