Anime Kaiba (episodes 1-6)
Kaiba is a very visually strange series- this is good. In an era of increasingly cookie-cutter animation styles, it's easy to appreciate a visual style that can be roughly approximated as Osamu Tezuka meets Robert Crumb. The coloring style is simple but very distinctive, and even characters drawn with the same basic template are quite easy to distinguish.
The plot as well is ominous but at the same time incredibly intriguing. The first episode begins with the amnesiac Kaiba not having any idea what's going on, with the only clue he has of anything the locket he wears around his neck with a blurry picture of a girl in it. The viewer is dragged along with him as he's chased through a destructive, dystopian world where we soon learn that memories are king, and the main outlay of the upper class. s Kaiba leaves the planet, he doesn't know what's going on- but neither do we. But we'll likely soon find out.
The next several episodes have Kaiba exploring various planets where we get a strong sense of good worldbuilding. Some of them are dumps, other are tourist paradises. All of them revolve around memories as a discrete transferrable quantity, some moreso than others, and all of them have disturbing implications. But in spite of the largely self-contained nature of these episodes, the viewer gets a strong emotional impact from watching the characters deal with their issues.
Simply as a matter of visual spectacle and short storytelling, it's hard to understate the value of the first half of this series. It's Walking The Earth, but with the odd twist that the character doing the walking is nearly entirely helpless and at the mercy of others. Kaiba is forced to do some morally underhanded things in order to survive, with the only positive point being that the people he undercuts really aren't very good people, either. At the end of the sixth episode, we're left wanting for more, as it definitely seems something must be done- but as of yet neither the viewer nor Kaiba has any idea what that might be.
Anime Kaiba (episodes 7-12)
By the halfway point in the series, we get back to the main plot. And unfortunately, not only is the main plot is absurdly convoluted, it has nearly nothing to do with the first half if the series. The subtext of the dark mystery of a universe with transferrable memories is dropped in favor of a bizarre adventure concerning Warp, King of Memories, and the power struggle over the domain he controls. Memories go from thought-provoking Speculative Fiction to a plot device used in relation to the power struggle. It's a big disappointment in many ways- the main one being that the rebel forces, which had first been mentioned in the second episode, are described as terrorists who attack memory tanks. We even have an episode where Kaiba meets one such rebel. But the reason for these attacks ends up going largely unexplained- it's not at all clear how they're supposed to assist in the rebel's goals.
What gets even worse treatment, though, is the sub-plot about the girl in the locket. Eventually, the full details of this relationship are explained- and it's a complete letdown. Again, it wouldn't be so bad, except that in an episode in the first half of the season, Kaiba meets her but doesn't realize it until the end, as neither of them are using their original bodies at that time, and the portrayal here is astonishingly poignant. The ten minutes spent in a later episode explaining how they came to know each other before the series starts comes off as incredibly cheap by comparison, and entirely unworthy of the emotional impact garnered by the spoiler'd episode.
Another problem is that a whole new set of characters is introduced in the second half of the series. None of them are given enough characterization for the viewer to really care about them, and the storm of reveals in the last few episodes comes off as extremely bland as a result.
I think if this were a 25-episode series a much better job could have bee done. It's hard to escape the feeling that eighteen episodes worth of material were crammed into just six episodes. As is such, I recommend watching the first six episodes, and then quitting while you're ahead on that high note.