Planetes is a masterpiece; a standard for realistic sci-fi, drama, romance, comedy and more.
A mature show detailing the lives of adults in an interesting setting, Planetes is as far removed from standard classroom anime as possible.
The show begins and contains a great deal of SOL comedy which slowly morphs to include more romance and drama. A grounded and realistic portrayal of sci-fi is a plus, with interesting plot points and world building to help get engrossed within the anime.
The SOL comedy slowly rises until a dramatic, emotional climax: believable, intelligent, and endearing, the show grows to present characters one can connect with and care about.
Ultimately, an outstanding show which is a must see for any and all viewers interested in : realistic science fiction, sol comedy, emotional drama, grounded romance, or a generally mature show far from the standard high school anime.
TLDR: MUST WATCH, particularly for adults or viewers interested in a more mature story.