Almost everything Yoshio Sakamoto has said about the Metroid Prime series.
Metroid Prime & Metroid Fusion Staff Interview - Nintendo Online Magazine - March 2003
http://www.metroid-database.com/features/nomsakamoto.php
Sakamoto-san, you supervised Metroid Prime and were in charge of directing Metroid Fusion. Prime was the series' first first-person perspective game, but...
Sakamoto: When I heard of the project, I was also bewildered. Because Samus is a relatively popular character, I didn't think it would be a good idea for her to come out in this form. But they showed it to me partway through development, and they had the Morph Ball, and the shape of Samus appeared to feel good. It had a cool world, and I thought it would do well. I think they finished it nicely.
About where in the timeline is Prime set?
Sakamoto: The story takes place between the first one on the Famicom Disk System and is followed by Metroid II. I had the idea to make it separately as a gaiden [side story], but wouldn't it be a cop-out to call it a gaiden? Because of that, I consulted with Tanabe, and things fell into place very naturally. The local staff worked on it really hard, it serves as part of the series, and I think they completed it very well.
Metroid designer Yoshio Sakamoto speaks! - CVG - 2003
http://web.archive.org/web/20121025...sive-metroid-designer-yoshio-sakamoto-speaks/
Sakamoto: I think my involvement with Metroid Prime II is like my involvement with the first one - I am advising them as to what kind of flavour they have to adhere to, and the kind of storylines possible - Retro Studios comse up with the story and I say: "Yes, it's the kind of story that's consistent with previous Metroid games" or else: "No, it's got to be changed like this".
Of course, whenever Retro is working on the Metroid games I need to supervise; I'm the person who receives the reports, to find out what's going on and how the title is progressing.
E3 2009: METROID: OTHER M HEAVY ON ACTION AND STORY - IGN - 2009
http://www.ign.com/articles/2009/06/04/e3-2009-metroid-other-m-heavy-on-action-and-story?page=1
Yoshio Sakamoto: One thing I need to explain is that I was really not that involved directly in the development of the Metroid Prime series. What I was involved in was the development of the initial NES Metroid, the GBA Metroid, Super Metroid and then finally Metroid Fusion. And within that timeline, the Other M story will take place between Super Metroid and the Fusion stories.
The Elegance of Metroid: Yoshio Sakamoto Speaks - Gamasutra - April 2010
http://www.gamasutra.com/view/feature/132721/the_elegance_of_metroid_yoshio_.php
Now, the Prime series was made by Retro, of course, and, being a different developer, they had a very different worldview for this game. You can say it's still the same Metroid, but it's a different, original concept. There isn't necessarily a direct connection between those initial concepts.
Metroid: Other M - Yoshio Sakamoto Interview - Gamespot - Sept 2010
http://www.gamespot.com/videos/metroid-other-m-yoshio-sakamoto-interview/2300-6276545/
Sakamoto: Metroid changing developers happens to be very natural to me. For example, as far as the Prime series by Retro Studios is concerned this [The Metroid Prime series] is actually another Metroid series. And I have had minimal involvement in the process of its development.
Q&A: Yoshio Sakamoto, Yousuke Hayashi on Metroid: Other M - Wired - June 2009
http://www.wired.com/2009/06/metroid-interview/
Sakamoto: You might be aware of this, but I actually wasn't that involved in the development of the Prime series. The goal in creating Metroid Prime was to create the ultimate first-person adventure, and I do think that Retro was able to do that. My approach, my concept, is a little bit different in terms of gameplay. And the story I want to tell with Other M can't be achieved with that approach. So I think my take on this project is quite a bit different than Retro's.
Wired.com: So, then, what is your vision of the ultimate Metroid game?
Sakamoto: Within the greater Metroid series, the Other M story will tie together the stories that took place in Super Metroid and Metroid Fusion. One of my goals is to present Samus as an appealing human character, and that involves explaining a little bit about what happened in her past as well as the characters that influenced her. The story will play a big part.
Interview: Metroid: Other M producer Yoshio Sakamoto - Joystiq - March 2010
http://www.joystiq.com/2010/03/12/interview-metroid-other-m-producer-yoshio-sakamoto/
Q: Retro obviously produced the Metroid Prime series; very successful, very influential. Do you consider this a reboot of the series after Metroid Prime? Is this the direction for future Metroids or just another direction?
Sakamoto: The games that I've been involved with in the Metroid series have been on the NES, GameBoy, Super NES and the GBA. I actually didn't have a lot of input on the Prime series. But when they're doing with Other M here, it's not so much a different universe, it's just a different part of the story. You can't say that there's no relation here; it's probably best to think of them as being in parallel in this world.
Q: What, if anything, has the team learned from Prime?
Sakamoto: I've been working on 2D Metroid games all the way up until now, so when we had a chance to see the Prime games, which suddenly take the series to the 3D space, we realized people found it to have a really good visual impact, and they really did want that kind of enhanced visual experience. And so, I have to say I'm certainly influenced by people's desires in that direction. There are some points in Other M that are going to feel a bit like the Prime series in terms of the visual experience they offer. But what we're really trying to do is bring the ease of play you found in the 2D series forward. But certainly Prime was a very cool series and we've taken some notes there.