Although I only gave it a slightly higher-than-average score, there's plenty to be entertained by here.
Story: A high school girl, Marika, finds out that she has the chance to inherit her father's Letter of Marque and become a pirate aboard the pirate ship Bentenmaru. After accepting the position, she goes on various adventures, and the story basically takes place in a series of problem-arcs. One of the things I really liked about the arcs was that they alternated between her pirate life and its problems and her high school life and its problems. I thought that this set up made for a much more believable portrayal of a girl trying to be two things at once, and Marika's strong yet humble personality carried her through both stories well.
I was initially really disappointed that the pirates didn't do much more than put on "pirate shows" for cruise-liners. If that had been the extent of the story, I probably would have given it about 2/10. However, Marika undertakes a few more unusual jobs, eventually leading us to discover that the world of galactic politics is not as stable as we may have been led to believe. The ending especially made up for my initial disappointment, with the pirates coming together to do real pirate work, with plenty of hints that their job is not over yet.
Another thing I really enjoyed was the lack of a love-story subplot. Yes, there were the two lesbian side characters, but the drama surrounding that only lasted for a couple episodes and was anything but melodramatic. Among the main characters, a love story was absent, and I think that focusing on the adventures was a good choice to make, although any second season of this show might do well to introduce a love interest for Marika to spice up the pacing.
Animation: I'm not an expert on this stuff, but the CG scenes of spaceships didn't seem too floaty, and I think that's a good thing (if you've ever been on a boat, you'll know that moving large machines around is a rather hefty endeavor). I liked the character design, and the use of color was appropriate: brighter pastels for the school/planetside life, and darker, deeper colors for the outer space/political-intriguey parts.
Sound: I'm only mentioning this because I really liked the in-show music, which was vaguely Celtic and, I thought, fit the atmosphere quite nicely.
Characters: Although there wasn't a lot of character development (where the characters grow as human beings), the characters were fairly complex. There were also plenty of intriguing characters that I'd love to know more about: Chiaki's father, Ironbeard, Quartz Christie, the chef brothers, etc etc.
Overall: Okay at first, slow but interesting enough in the middle, and definitely redeeming qualities to the end. I would be willing to give a second season a chance.