Man, these go quick.
Volume 3 is mostly filled with one gargantuan (by Astro Boy standards) story that remains one of his most popular. It probably has the most really big, crazy-looking, battle robots that Tezuka ever invented for an Astro Boy story. It's also full of fight scenes--definitely the most action oriented story so far, but a lot of fun. On top of that, the villain is huge and scary-looking, but basically seems like a kind of child conscripted into battle, or some such, which makes it all a bit sad. I would've liked it if the real villains had had some kind of comeuppance at the end, though.
There's a little short story at the end that deals with robot civil rights, basically, which is always interesting. It also has some of the best-drawn chaos I've ever seen.