Gameplay-wise, the game was decent, but it could've been even better if it had nunchuck support (seriously, why the hell were they thinking), i hated switching the Wiimote from horizontal to vertical. and the level design was pretty meh, it was linear but it wasn't like Fusion's atmospheric type of linearity, it was extremely devoid of inspirtation. and not to mention the power-ups, getting them felt useless compared to past entries where you would genuinely feel as though your power increased, where in this game Adam orders you to use whatever.
Story-wise, we have a HUGE problem. how the hell can they expect us to put up with a cry-baby Samus when in the previous game that was released (Metroid Prime 3: Corruption), Samus doesn't hesitate to kill the hunters, even though they were her partners.
as for the Baby, in Super Metroid, she gives it to some researchers for experimentation purposes for crying out loud, why is she suddenly mentally and emotionally scarred due to it's death in this game?
and Adam, his character in this game was a completely missed opportunity IMO. in Fusion, Adam was described as a brave soldier or whatever, he stops Samus from blowing up the ship and herself with it, and he seemed like a possible love interest. in Other M, he's a jerk, no other way to put it. he blew up his own brother, and stopped Samus from using her own abillities. Samus and Adam's relationship in this game seemed like a school girl obsessed with her senpai type of relationship, unlike Fusion were it was mutual, mature interest.
overall, the game is decent-good when viewed as a standalone action game, but that's not what it was meant to be viewed as, it was meant to be viewed as a Metroid game, and in that regard it failed to live up the rest of the series, even moreso than Pinball.