After mentioning in passing how much I liked the series when it aired, I’m way behind in wrapping that up – so I’ll keep it brief.
The anime is a strong adaptation of the manga – the eyecatch stills unobtrusively build up the background of the world, the Titans look and move abnormally, and the story alterations are generally improvements rather than just being filler. In particular, the training scenes are presented chronologically, and you get to see tough-guy Levi’s soft side (not that anyone finds out), and Erwin’s capture plan features more of the characters and tactics introduced previously. One strange change is the ending; in the manga several characters discover the secret of the walls, while in the anime it’s just shown to the audience.
The main weakness of the series is how its pacing slackens in some of the middle episodes, where you start wanting the characters to stop yelling and acting shocked and do something. Additionally while the main combat scenes are spectacular, you can see how they saved budget during other scenes.