This anime entirely eliminates one of Houseki no Kuni's (the manga) stand-out flaws. Unlike its roughly drawn, sparsely backgrounded manga counterpart, the anime looks amazing and uses CGI to its advantage, rather than as a tool to drive down animation costs.
The refraction of the gems' hair looks amazing, the colour palette is bright and beautiful (though gets a little ugly in the later episodes), and the music gives a whimsical, almost-Ghibli vibe that you can never go wrong with. Some of the fight scene sound effects are pretty questionable, but the music makes up for it. We can finally experience Houseki no Kuni in a
form where the characters are (usually) on-model, instead of rarely.
Unfortunately, if, like me, you are one of those fans initially drawn to Houseki no Kuni by Phos's magnetic personality, you might not find much reason to keep watching after it's gone. I didn't. The action scenes never interested me. I never thought the mystery behind the three races was particularly profound or interesting. I already know what happens and I still don't care for it.
Keep in mind that four episodes of the post-winter arc is nothing compared to the some-40 chapter long drawn-out, boring slog the manga turns into.