After reading a couple other books by Heinlein, I was both shocked and energized by Starship Troopers. Who would've thought that Heinlein would write military sci-fi? It has a hard SF edge, running through military training and leading into combat against a truly overwhelming foe. The element of refusing to surrender is truly motivating. There is great storytelling and the characters are very real (some you love, so you hate, and you enjoy doing both). Highly recommended!