It's a pretty weird SF series by Masaaki Yuasa, one of the most original creators in anime. It's as stylised as if it had been made 50 years ago. Yuasa likes that kind of thing.
The plot, though, is a bit impenetrable. The information's all there, sure, but you'd need a second viewing to have even a hope of catching all of it. You're thrown in at the deep end and expected to sink or swim. For these characters, memories and bodies can be bought and sold... if you're rich. You can sell yourself for money, or you can buy an artificial body. There are memory tanks. There are guns that gloop you. A life can be stored on a cone the size of your fingernail and plugged into a spare body, if you can find one. Kaiba is one of the names of our hero... and also of a predatory memory-eating plant, and is also the Japanese word for "hippocampus", a part of the brain that's crucial for memory.
Characters can drift from body to body. You won't always know who you're talking to. Our hero doesn't know who he (?) is, or indeed anything about himself beyond the Tom-and-Jerry hole in his body and his weird tattoo. The episodes aren't shown in chronological order.
Then, in addition, you have the art style. Apparently, it's inspired by the claymation game Neverhood, which was huge in Japan and known as "Klaymen Klaymen". It also looks a bit Tezuka. What it doesn't look like, even remotely, is any anime made in the last forty years. It's fascinating, but it's yet another Layer of Weird. It's deliberately making the show look childish, despite being a story of death, grief, greed, identity, love, betrayal and loss of personality.
Oh, and it has some beautiful music.
Is it good? Yes, very. It has some strong episodes, e.g. ep.3, Chroniko's boots. (Evil is done by someone who's not evil and grieves for it afterwards.) The disorientation factor also makes the show a fascinating experience, albeit one that's not for the casual viewer. Put this on BBC1 at tea time and by the end you'll only have fifty people still watching... but they'll probably phone each other up afterwards to discuss it.
Is it great? I wouldn't go that far. It's a strong, interesting SF show that's fairly hard to process. No compromises have been made for the audience. That's part of its charm, obviously, but that still means you're going to miss a lot on first viewing. The ending doesn't explain everything and you probably won't even realise, because it's hard work to understand it in enough detail for nitpicking.
There's a lot here to discuss. What was Yuasa going for when he combined this simple, childish art style with this dark, complex storytelling? Maybe it's reflecting the content? (A culture where people replace their bodies and their memories is basically deleting bits of themselves they don't like and replacing themselves with happier, jollier versions.) Maybe he was trying to say something about how we consume stories and the assumptions we make based on shallow first impressions? Or maybe he just likes cool art styles? There's nightmare consumerism, e.g. bodies thrown out with the trash, or the symbolism of an impoverished young girl literally selling her body. There are saboteurs, rebels, dictators and heavy-handed cops, any of whom might casually execute people they don't like. There's a sea of unclaimed memories.
It's dense, heady stuff. I don't know if I'll rewatch it, though.