The protagonist from another world becomes stranded in a new world, the protagonist adapts to the new environment, the protagonist begins to prefer new world over old one, and then the protagonist saves the new world. Many anime use this setting, with only small variations, including Inuyasha, Zero no Tsukaima, Dog Days, and Hataraku Maou-sama. I enjoyed all of these to a certain extent (except Dog Days; was just too bizarre for me), but none of these shows really focused on how the protagonist struggles to adapt. After one or two episodes of the protagonist being awkward, he/she becomes used to the new setting, and the plot speedily moves on. Suisei no Gargantia manages to set itself apart from these by expanding on the difference in culture between Ledo (main character from militaristic space colony society who fights off alien squid race that is trying to annihilate humanity) and the people of Earth. This does not justify the problem Suisei's story has. Many episodes do little to progress the plot, which is, overall, very basic and predictable.
Character designs, mecha animation, and many panaromic shots of the settings are done very well. Quality isn't always consistent, and the animation isn't worthy of a 10/10, but I had no major complaints.
Sound, in terms of theme songs, background music, and voice acting, was of average quality. Nothing particularly stood out. In fact, the opening felt like it was meant for a slice of life anime rather than a mecha show.
This show makes every one forgettable and insignificant. Ledo is the only one that really develops (and they are very basic changes that only exist because they were necessary for the plot to make sense). Amy (main female lead) is simply a friendly girl whose presence made little difference. Pinion (a minor character) had some potential, but didn't learn anything in the end, and is therefore one-dimensional as well.
I would not recomend this to anyone. It isn't memorable, and will likely be forgotten in a year.
TL;DR: I guarantee there are plenty of better anime to watch out there.