[AgileSiamang7]

Brotherhood likely gets the amount of love it does for a simple reason: viewers like to have the "real" adaptation first before anything else comes out.

It's one of the reasons Harry Potter fans get so annoyed when the movies are shorter than the books, or have parts left out. They don't get to see their favorite scenes, or a really important scene the director chose to leave out brought to life.

If the 2003 FMA was released later rather than first (which would likely mean that Brotherhood in this case would still have filler episodes, like the big 3, to give the manga time to outpace the anime), then some fans may be more forgiving because it would be treated as an intersting alt. anime, rather than a "lie" of an adaptation.

Even if you don't like or care about Attack on Titan, imagine if that chibi anime that's out know was the first adaptation of the manga: how pissed would the Titan fans be, that they weren't getting the 'true' anime they wanted?

...though to be fair, many of my friends who are into AoT started with and prefer the anime.