The show borrows heavily from the Heinlen book, except for in most regards it does things better. And unlike in other kids shows, there are casualties. People are impaled by bugs. People have their spines snapped in half and are left as paraplegics for the rest of their lives. Entire squads are wiped out in unpleasant ways.
Cities get carpet-bombed.
People deal with decidedly-adult issues, including xenophobia, bigotry, love, death, and how much the civilian population should truly know about the war. I can't help but think that the issues the show deals with would make Heinlen proud. The character development is excellent, and the plotline both complicated and realistic. Naturally, adults who love good sci-fi, or just love good writing, love the show, and have given it what fanatical support they can. It seems if you're over the age of 13 and aren't braindead, you'll probably fall in love with the complexities of this show.