I didn't know quite what to think of Stellvia until the ending plot arc. This story is more or less a two part tale. The first part deals with schoolgirls on a space station. That concept by itself would have gotten boring by episode 12, except for the fact that the series transitioned to part 2: which was something much more interesting and used the material from part one quite well.
So thematically, this is a slice of life show about a teenage girl who wants to go to space and learn how to be a pilot of spaceships. Plot wise and character development wise, this is about a teenage love story in space juxtaposed against a... well, spoilers aside, it's an interesting problem they face up in space. I don't group the love story in the theme group because it isn't really used as a theme: it is more like a plot device to heighten people's tension as the characters deal with the problem: Heroic Age's Princess Yunos and Age, now there's an entire song and ED devoted to those two. People's performance tends to decrease if they have relationship problems: unlike in certain Hollywood movies, a romantic problem doesn't result in a job loss or loss of some insignificant social status. A disruption in a person's mental focus and concentration is lethal in space. In Stellvia, romance eventually becomes part of the plot development when it comes to operations in space.
Here is some explanation for why I promote things from 4/5 to higher ranks. I did not particularly like the main character nor the character designs. There was no beauty in them, compared to some other artwork I have seen in anime. Yet my standard for rating a series depends upon whether it had something innovative or demonstrated an ability to take on high risk challenges, without falling down too often. Stellvia, based upon the romance, the slice of life comedy, and the space station setting, was worthy of a 3.5/5 or 4/5. Above average or worth watching, respectively: both of these have flaws as well as points in their favor. But something has to do more than interest me or make me dislike it, for it to get a higher score than 4/5. Whether I liked the character or the artwork, didn't really matter in the objective sense. What mattered was whether the series could pull off their plot line without me detecting any inconsistencies or flaws once the last episode ended. If it had music, art, story line, epic plot, or great enough characters to overcome its weaknesses, it's almost guaranteed a promotion to 4.5/5 or 5/5. If my emotions were smooth and consistent with what the show tried to get across, it will get a promotion above 4/5, assuming no erroneous mistakes show up. This is independent of whether I like the ending or not, or some of the characters. So this is why irregardless of the artwork creating no draw in me, I gave this series 5/5. The story progression was that good and interesting: while there were some shaky parts where I wondered whether they could pull it off or whether they were being just a tad too melodramatic by intermingling someone's private life with their professional job, it was not enough to make me detect a critical error. This suspense ended up bolstering the great ending.
I greatly liked the ending and rewatched it a few times. The beginning and middle portions I avoided rewatching simply because the atmosphere is too much like high school. Immaturity and growing pains is only tolerable for so long for the sake of the plot and story development. There's no need to go over it when unneeded.
5/5 Excellent ending, interesting plot development, rich world building, and a novel coming of age story.