Unlike the more popular Monster or 20 Seiki Shounen, Pluto has a less intriguing plot but a much greater level of emotional impact. Never having been a supporter of the "androids who fall in love are worthy of being bestowed with human status" concept that most works of fiction in this genre flaunt in an utterly shameless and ridiculous fashion, I was pleasantly surprised to discover that there were no such petty, shallow ideals here. Certainly, these robots resemble humans -- but it is not the ability to experience sexual desire or romantic love towards a human being that grants them 'humanity'; it is the fact that they are capable of the compassion that most 'real' people are unable and unwilling to show towards their fellow man. It may strike one as being a cliche, naive and childish idealism (and I suppose in a way it is) but it's no less effective because of that. And certainly less brainless and simplistic than the typical "S/he fell in love and therefore s/he is a wonderful and complete human!" (Unfortunately, this is the path most authors take in their attempts to solicit the readers' sympathy towards any non-human, androids not excluded)
I can honestly say that Pluto is one of the handful of stories (in any medium) which succeeded in inspiring such powerful, melancholic and empathic emotions within me; something that more favoured and widely-read series with similar themes such as SaiKano and Ai-Ren failed at spectacularly.
The technicalities of the plot were interesting, though slightly weak compared to those of Naoki Urasawa's other acclaimed thrillers. The conclusion in particular was sub-par -- while it did not detract from the emotional and intellectual impact of the tale, the resolution of the mystery involving the robots, their creation and subsequent destruction was disappointing. The series certainly could have done with a few more volumes worth of clarification. I suspect the shaky ending may have been a flaw that stemmed from the mangaka's attempts to remain faithful to Osamu Tezuka's original work; but since I have no interest in reading Astro Boy this hypothesis will have to remain unconfirmed.
While the art is not particularly special, beautiful or elaborate, its bland, unattractive quality provided a very appropriate atmosphere that accentuated the bleakness and hopeless mood permeating the story and its characters.
Overall -- it could have been better, but I still recommend Pluto to anyone interested in seinen manga with a sci-fi touch and intelligent musings on human morality. As long as you don't expect a romance-packed, violence-filled thrill-ride, you should find it at least moderately satisfactory.