User blog comment:Omega natsu2/Chapter 356: Tartarus arc - Prologue, Predictions./@comment-4829046-20131013104810/@comment-7418318-20131013152049

To list everything that went wrong with the anime would be too much to state here and now, but you could check out the Shingeki no Kyojin wikia to find detailed analyses (and rants ;) ).

Like here or here for example.

Not all anime-only content was really bad. For example the scouting legion having to dump the bodies of their fallen to escape fit well into the story, but unfortunately the last two episodes are a different story.

Some of the changes to the Magi anime might not exactly have been great, but at least they never contradicted or otherwise undermined the character development or long-term direction of the story.