For most people Metroid games mean isolation and exploration, while Samus as a character isn't really more than a silent suit of power armor. While I definitely think that those characteristics were very important aspects in the series so far, I'm not going to naively think that the franchise will never try anything new. Some people might be satisfied with a few new worlds to explore in the traditional Metroid fashion, but personally I find nothing wrong with Nintendo trying to take the series in a slightly new direction.
If you want to be alone on an alien planet with nothing more than your Gravity Suit then you have Metroid, Metroid II, Super Metroid, Metroid Prime, Metroid Prime 2, and Metroid Prime 3. To a lesser extent you even have Metroid Fusion (which I personally loved; I have yet to find a more atmospheric game on a handheld console. Some of those SA-X segments were terrifying). In any case the release of Other M in no way reduces the quality of those seven games (just like how Metroid Prime Pinball didn't destroy the series either); it is simply trying to flesh out the story and the character a little more. Honestly, what else could they do with the franchise? Where else could they have gone? They been doing the isolation thing for decades.
Besides, many of the people playing Metroid today (in fact, I'm willing to bet that MOST of the people playing Metroid today) don't share the same expectations as you guys do. I'm one of them. I don't think giving Samus a voice is a bad idea. I WANT her to be an actual character because Mario and Link already play the silent protagonist. Samus actually has the potential to be a little more interesting.
People are always complaining that Nintendo never does anything new, and yet when they do people bitch some more. I understand if you legitimately dislike the story or the dialogue, but to complain simply because story and dialogue exist AT ALL is pointless. If you don't like it, ignore it. Don't play it. Problem solved.
PS. Sorry for the wall of text! It should also be noted that I have not yet played the game and I could end up hating it too
My rant is probably a little too late since most people have moved on to complaining about other aspects of the game like the controls. I just started typing and couldn't stop myself...