Amazing. Absolutely amazing. Both the storyline, but also the characters. This anime also has one of the best art styles I've ever seen. I really reccomend watching this anime, but there is involved blood and many deaths.
Personally, my favorite thing about Attack on Titan is mostly the animation. Many of the characters are amazing too, but my favoirite is Annie Leonhardt, aka 'The female titan.'
I enjoyed watching this anime very much!