I actually kind of liked it. While not nearly as good as Super Metroid or the Prime series, it did try some interesting new things and I'm sure it would have had much better reception if it didn't have to live up to its predecessors.
Aspects of the game I liked were level design, the return to (sort of) 2D and the action sequences. Parts I didn't like were the uninteresting story (to be honest, none of the Metroid games really had much of a story; but at least they didn't bother with many cut-scenes and such), the boring characters, the pointless 'pixel hunt' moments.
The fact that the Adam-character had to approve of you using any of the weapons you already had on you was also a very bad design decision. While letting you obtain the weapons traditionally wouldn't change much gameplay-wise, collecting items is an important staple in Metroid games (or Action-Adventures in general) and gives players a sense of accomplishment and growth as the game progresses. Coming up with another lame excuse as to why you lose all your weapons at the start of the game would have been a much better idea.
The thing most controversial about the game was Samus's character, which many people really disliked. This is pretty understandable, as she has been a blank slate (like Link from LoZ) in most games and people developed different personal interpretations of the character.
However, the way Samus was represented in this game (including the jarring 'daddy-issues') was pretty faithful to how she was established in Metroid Fushion. Probably not that many people played it, since I can't remember hearing the same complaints about that game.
