User blog comment:Omega natsu2/Episode 184: The Country, Until Tomorrow, Review./@comment-110.20.169.85-20140531044232/@comment-4449950-20140531044744

The anime never outshines the manga mainly due to one reason: the fact that Hiro Mashima's art is so clean and gorgeous. With other manga/anime series, the animators can often match and sometimes surpass the art of the manga, and then because they add colour, voices, music and movement the anime is incredibly successful. Here, it's a different case. The anime does add voices and great music and this is nice, but people who read the manga can't get over the fact that the characters just look nowhere near as clean and pretty as their manga versions. As such, though the anime is by no means bad, it does not hold a candle to the manga, and is heavily criticised by FT manga readers in this aspect.

Well, at least this is the general reason for why the anime is considered "bad". Everyone has different opinions of course. I for one don't think the anime is bad, but it certainly doesn't come across as nicely as the manga.