Tetsuwan Atom

Astro Boy is a historically important manga/anime, if only because its success helped in no small part to establish the Japanese animation industry and helped familiarize Western audiences with Japanese media (although it would still be a few decades until it got really popular).

While this is by no means an outright terrible series, its not that good either. Keep in mind that most of the series was drawn with small boys in mind as its intended audience and it shows very clearly. Not to mention that it was released almost 70 years ago, meaning that various parts of the manga have not aged very well.

The art is pretty good but the stories are very simple. While they do often address serious issues like intolerance and violence, the stories they feature in are very simple with predictable resolutions and very little depth. Most of the stories are episodic, which means that the quality of the manga changes with every chapter (although some of them are actually good) and continuity isn't something that's regarded seriously. The characters are flat and boring, if not completely unlikable. The supporting characters have little to no development from their initial introduction and the villains are mostly just there to serve as punching bags.
Astro Boy himself is fine but there's nothing really remarkable about him.

Unfortunately, its historical significance is the only reason I would recommend anyone to read this.

Manga history! This should really be read by everyone.

The manga doesn't really have an overarching story, but rather just a collection of stand-alone chapters. However, these chapters can be really long, like half a volume long. I would recommend reading all of them but it can be a bit of a drag sometimes since not all stories are especially interesting. One of the real essentials is one of the few real arcs, "Once Upon a Time" spanning volume 6-8. The arc is also a good example of the darker side of the manga. The stories are often about the nature of humanity, violence and war. There's usually a lesson to be learned at the end.

The art style is childish, but it really is excellent. Tezuka has a really cinematic style and is great with shadows. The characters are also great but unfortunately most of the main characters just don't get enough development or relevant screen time. My favourite characters were Astro Boy himself, and his creator Dr. Tenma. Dr. Tenma is not a good guy but he's not fully evil either, he's a very morally grey character. Dr. Tenma doesn't appear that often, but whenever he does, it's a highlight. The one-off characters are also really great, and all have their own back story, motivation och development.

Unfortunately the manga overall is very up and down. I think for younger children it doesn't really matter, but for an adult some chapters don't really leave an impact.