For the topic at hand:
Given that they use Samus's sex as a reward to encourage high-level play in those games, do you acknowledge that we are not rewarded in the same way in Metroid Prime, Echoes, and (mostly) Corruption?
I just chime in here, because I didn't get a response to my post despite an announcement that there will be one. *EDIT: Looks like I got one while typing this post.*
I have never viewed the "Samus without armor" reward as her sex being the reward, but rather as a glimpse at the person that wore an armor the whole game. The reward isn't to see a woman, it's seeing the character you played as. The reward is to see a more elaborate ending sequence, even if it is just a short extra scene or a slightly changed scene. Since this happens after the game is over, these scenes that show Samus without armor do not hurt the immersion of the games. For the time I play the game, I feel that I really am this character. Once the job is done, it's time to return to real world. When I see Samus without her armor, I cease to be her. And that's perfectly fine, because the game is over.
That's why I don't have a problem with these scenes. They take nothing away from the games (Metroid, Return of Samus, Super, Prime trilogy). The problem of Zero Mission's Zero Suit is the altered gameplay for that section. Fusion's problem is that Samus talks to the player throughout the game. In these moments you cease to be Samus. Other M adds extreme sexualisation of Samus throughout the game on top of her talking a lot, that's why the game doesn't feel right from the perspective of immersion. The game has also a lot more problems beyond that.
The first time I viewed Samus Aran as a sexualised character was in Echoes' ending sequence. The problem wasn't the Zero Suit, her face or her now yellow hair (her character model looked vastly different than in Prime). Her breasts got pumped up to the desired American standard size. That was pretty shocking to see, but it's just an ending sequence. The guys from Retro Studios had some fun and I never gave it any more thought. Something as short as that doesn't hurt Samus as a character. Corruption scaled her breast size back a little. What exactly was this topic about again?
Oh right, it's about the player being Samus. The immersion starts to vanish as soon as the final boss is defeated or the ship is reached within the time limit (depending on the game). Why? Because the game takes away the control from the player. Whether you see Samus in full armor or without armor in these final moments doesn't matter. This is the point in the game where you cease to be Samus, because you know that the game is over.