Sungeki no Kyojin ("Spoof on Titan") is a yonkoma—a four-panel gag manga—based on the world and characters of the manga Shingeki no Kyojin ("Attack on Titan") by Hajime Isayama. It very loosely follows the events of the main series and builds up on its deep characterization, serving it with some of the most fun and tasteful comedy I've seen in a while. See all of your favorite characters of SnK, most notably the 104th Trainee Squad and the Survey Corps, play out various scenarios that you (probably) wanted to see but never had the chance to.
Although Sungeki reads and looks like a typical 4koma—i.e., simplistic
in every respect—it is, for the most part, pretty well done. Characters' emotions are all carefully articulated, and feel true to the originals. I actually laughed out loud at some of the strips, which is already more than most comedy/parody manga and anime titles have managed. This, for me, is one of the rare few instances of a well-designed setting and a good light-hearted comedy writing blending into something more than the sum of its parts. Good job, hounori!
Of course, I *very strongly advise* to catch up on the the first few arcs of SnK before taking up Sungeki to avoid numerous spoilers.