The main problem with this game is that it´s not appealing to metroid fans (maybe to some but not to the hardcore ones), and that´s because of many reasons, one being the fact that developers named the game metroid prime when it has nothing to do with the prime trilogy, and of course it doesn´t help that the game graphics look awful.
But lets forgert about that one for a second, another reason I belive this game is terrible is because the characters.
There is so much wrong with federation troops as the main characters, for example in no game of the prime series have they been able to take down the main threats by themselfs, but in this game we are supposed to belive they can?
Another problem I have with this characters is that we have no idea who they are, of course we know they work for the galactic federation, but who are this troops that apparently possess the power to take down the enemies only Samus could in previous games without her? Did they help Samus in taking down the space pirates homeworld in the final mission of prime 3?
Of course the game is not a terrible idea, in fact I belive it could have worked a lot better this way:
They set the game after the events of prime 2 and before prime 3, the galactic federation calls Samus to do whatever the mission is, but since this is a co-op game we need another 3 characters to do the job, and instead of assigning three irrelevant, weak federation troops, the galactic federation decides to call 3 strong bounty hunters, Rundas, Ghor and Gandrayda (yes, the same trio that appeared in prime 3) each one with their own unique abilities.
Using Samus and the 3 bounty hunters of prime 3 would fix this game in so many ways, not only do we get 4 relevant character we can relate with, each one has different abilities so that opens a ton of gameplay possibilities, plus they get the chance to develope the character of Rundas and the other 2 bounty hunters, maybe explain their past and that kind of stuff.
That´s how I would have made the game, and I agree it should not be cancelled, that petition made a while ago was stupid, plus the terrible sales will let nintendo know bad they messed up.