The book is one of his "Juvenile" books, written for a teenage audience. Fast read with a, IMO shallow story line on top of a much more interesting world that he built. Book would probably take you an evening to get through.
I'm not unaware. My mother's side of the family considers Heinlein a saint. He was the author of note, the one to pay attention to, the inventor of waterbeds, the ubiquitous gift at every holiday. I'd read Space Cadet and Red Planet by 2nd grade. By the time I'd made it to Jr. High I knew ridiculous shit like Farnham's Freehold back to front. But then I started reading other authors and determined that Heinlein was basically a dirty old man with some interesting engineering ideas who fell for that exact same one-world-government libertarian bullshit that sci fi authors always fall for and by the time I'd gotten to the point where okay, let's read fuckin' Starship Troopers I just couldn't. I couldn't. I was so fucking sick of the man. I mean... he gets props for first using a space elevator in Friday, and more props for blowing it up within six pages of introducing it. But Heinlein's idea of what characters are for and my idea of what characters are for are so diametrically opposed that I really enjoy cheering on Verheuven's Starship Troopers BECAUSE it annoys the fuck out of my purist family. I owed flagamuffin Lord of the Rings. I gave it a go. I really did. But I know I don't give the first fuck about any more Heinlein ever so I'm gonna sit it out, thanks.