It was still based on the same core gameplay and in a lot of ways almost played like the Super Metroid in first person. It was that faithful to what the series was about that even the dramatic shifts you're talking about didn't alter the spirit of the series. FF isn't in the same boat at all; it's a mission based online team shooter. It has little connection to the series other than the control scheme and characters.
They may have some goofy missteps here and there, but the Metroid games generally are serious by nature and are probably the darkest main series Nintendo has. Their inspiration was Alien- an intensely serious film- and at times they can be frightening or violent games. It's not often that you see an enemy's face melt off in a Nintendo title:
One of the main hallmarks of the series is isolation- feeling lost and alone on a hostile world. It's that kind of tone that people play these games for. What they're doing with FF isn't really appropriate for the series- you're not alone, you're not exploring, and the presentation is way outside of the realm of this series- and it demonstrates that Nintendo still doesn't understand what the series is about at its core or what the fans expect from it.
Imagine a modern FPS-style Mario game where the characters are using actual guns and killing each other; it may be a fun game on its own if it's designed well, but it would be terribly inappropriate and just wrong to do with that character and series. The style of FF, both in terms of the visuals and gameplay, makes me cringe every time I see it. It was just a bad idea, and obviously fans weren't asking for a game like this.
.
..What?
You can't blame the fans for this situation. That's on Nintendo. They received an incredible amount of complaints about Other M not having real Metroid exploration and gameplay, about being too story based, about not having much atmosphere... and Nintendo's response was to release another story based Metroid without exploration and atmosphere, but this time on a handheld with cartoony graphics. It came about because Tanabe wanted to make a game to flesh out the lore behind the troopers, and the gameplay stemmed from that. It's unbelievable that after Other M this idea was pitched and Nintendo apparently said "yeah, sure, go nuts."
You could say "what's it to you, just don't buy it," but I care a lot about the series. The time they spent developing this could have been spent on a Metroid game people would actually
have been asking for- we could have gotten the first new 2D Metroid in
11 years, for instance.
None of this means that FF is a bad game on its own merits. It could be a really fun game, but that doesn't change the fact that it was a really bad Metroid. And, based on all the videos and hands on accounts we've seen, it doesn't really look that great even taken on its own merits. It's slow and clunky, and generally seems pretty cheaply made. I could turn the question around on you and ask why you're being so defensive about the game... does it really look
that great to you?