If you don't want to read much, I'll summarize a somewhat detailed paragraph on what I think about Houseki no Kuni overall before truly going in-depth about my thoughts on the series:
// REVIEW CONTAINS MINOR SPOILERS //
Houseki no Kuni is a fantastic series with powerful themes such as self-acceptance and finding ones-self in the world around them. The post-apocalyptic setting is very interesting to explore, character dynamics are fun and individual characters have clear personalities for the rather short 12-episode run time. The MC's character progression was satisfying to see as well. Most powerful element in this anime would have to be the visuals; absolute eye-candy, coupled with a great soundtrack as well.
This anime is a must-watch for everyone.
// IN-DEPTH ANALYSIS //
VISUALS:
An extremely powerful factor in the series to me; this is the best I've ever seen 3D look in an anime, Studio Orange has truly outdone themselves in that regard. Before watching the anime, I've only read one chapter of the manga, although the art is more unique stylistic-wise, the anime blows it out of the water when it comes to visuals. Incredible, fast-paced action sequences that never disappoint, the impact is clear and the momentum is visible and powerful. It also seemly has an endless amount of beautiful stills and shots, the color scheme is creative and the lighting just sets up for every frame to be eye-candy to look at. Houseki no Kuni is undoubtedly one of the greatest looking anime I've ever seen in my life.
MUSIC:
The music played throughout Houseki no Kuni perfectly captures the mood of the scene. One of the most memorable soundtracks to me is when the Lunarians attack, it's so mystical and spiritual, but doesn't sound outright threatening, which is perfect when you think about what the Lunarians are. Sadder pieces in the soundtrack are also placed very well and are effective in bringing out the best in an emotional scene. What an absolutely wonderful score.
PLOT:
The plot of Houseki no Kuni is quite interesting. It might be a bit jarring to be thrown into this post-apocalyptic setting without any real context, but it helps to have a certain degree of accepting the world in the story to be just the way it is, it serves as a great mystery that'll be explored more as the series goes on. The main focus in the anime revolves around Phosphophyllite trying to find their place in the world. The main theme of the story deals greatly with self-acceptance, and a purpose in life despite your weaknesses. Although the solution might not be clear and seem grim, it's ultimately a unique way of finding peace with ones-self. If Phos's solution seems disappointing to you, the story seems to set up Cinnabar as another way of confronting this theme.
CHARACTERS:
Somehow, in the short 12-episode run time, the series manages to greatly progress Phos's character, as well as the multiple side characters as well. Not every gem might've received sufficient development and progression, but that's expected. It's impressive enough that Houseki no Kuni manages to easily characterize a lot of it's cast with unique personalities as well as interesting character dynamics. Characters like Dia, Bort, Cinnabar, Antarcticite and Rutile have an impressive amount of characterization and development. In terms of character designs, they might all seem similar from the neck down, but it's fascinating how small facial features such as eyes as well as hair can impact everything so greatly, I was thoroughly amazed and how different everyone looked despite wearing the similar outfits.
Truly a GEM of an anime! (badum-tss)