My household loves the terrible movie inspired by the book, so I couldn't resist reading the book when I found it at a book sale, despite being warned that it bears very little resemblance to the movie. 
 And that's true. For one thing, the movie had a plot, which the novel only flirts with occasionally. In the novel, Johnny Rico joins the Mobile Infantry against his parents' wishes, muddles his way through bootcamp, then begins his career in the military. Characters pass in and out of his life and we're taken on a whirlwind tour through his story. 
 The whole novel seems to be a vehicle for the History and Moral Philosophy courses that Johnny takes at various points through his life, and where his teachers can rant about various theories. These were, mostly, at least interesting, but some were just weird - such as the rant about how much better our society would be if we reinstated corporal punishment (both as a legal measure, and for parents to use on their children from as young as babies), as if this were a thought experiment and not something that had actually been the case through most of human history. 
 The subject of the military was rather interesting, since it's so far out of the realm of my experiences. I've read a lot of books that talk about military events, but always from above, rather than what the experiences would have been like for the grunts. 
 It was an interesting book, but it was weird and overly preachy on philosophies that hold water about as well as a colander. There were no consistent characters to develop an attachment to (even Johnny was really more of a vehicle than a character), and there was little to nothing of plot. But some of the ideas presented were interesting, and Heinlein does construct scenery quite well.