While not exactly about terrorism, Zankyou no Terror has an artistically brilliantly story line. The calming music clashes with the tense nature of the anime in a beautiful sophisticated way. I actually studied the soundtrack before watching the show, as it came up in a music analysis class i take, so my opinion may be a tad biased. However, it is some of the most poetic piano music you can find in an anime.
The animation wasn't lacking but was nothing special. The character development sadly was lacking. While the characters were indeed unique, you don't really find out that much about the main duo. They lack depth and you never truly get a sense of who they are. They also don't really get the chance to grow as the series progresses.
The story was unique and well-balanced. The plot was well constructed and thought out, including twists when least expected and an appropriate usage of flashbacks. This story is distinct, complex and extremely compelling and was by far the selling point of the anime.