I do agree that the reaction to Federation Forces is a bit over-exaggerated, though I can't say I blame them. Hell, I was pretty salty once I saw the reveal but I'm over it now.
Expectations are extremely high after Other M's polarizing existence, and especially so when this new game bears the name Metroid Prime in the title, which is considered in very high regard. Not having a Metroid game in 5 years (or 8 years for a good Metroid game) doesn't help either.
Honestly, I think the negative reaction is more so because of the way it was presented. The Troopers are all chibi-like and everything looks so colorful and it just doesn't mix with the art style and atmosphere that Metroid has created throughout the years. That soccer game, or whatever it is, also feels like it was slapped into Metroid for no reason as well.
It doesn't look, nor feel like a Metroid game to many, and I think that's where all the negativity is mostly coming from. If they had announced that a main Metroid game is being worked on as well, I think things wouldn't have been as negative.
I don't hate the game but I don't like it either. I'm pretty ambivalent on it, but I do understand where the hate comes from.
Just some random thoughts~ :3