Parish interview with Sakamoto from Nintendo and Hayashi from Team Ninja:
http://www.1up.com/do/previewPage?cId=3174587&p=44
1UP: When I think of the two series, they seem very different. Metroid is very slow, methodical, exploratory, while Ninja Gaiden is very fast, violent, and action-oriented. How do you reconcile those two and create something that takes advantage of your strengths, but still feels like a Metroid game?
YH: We want to try and take the best of both. As you progress through the game, there will be more action-oriented, faster-paced sequences. But then you'll have your careful, exploratory parts of the story as well. We actually used it to our advantage to try and marry the two concepts together.
YS: When I brought the proposal to Team Ninja, I had no idea what their response would be. As we progressed through development, of course there were differences of opinion, but we were able to work through those and ultimately create something that's better than either of us could have expected. It's been a really collaborative, creative process, and I feel that the result is something that's very positive.
1UP: Ninja Gaiden has a reputation for being extremely difficult, and while Metroid has been difficult, it doesn't pride itself on breaking players. Do you intend it to create a challenging Metroid, or will you go easy on us?
YH: Our goal isn't to make something that will break players. It's for Metroid fans and new players alike, so we're not taking the same approach as with Ninja Gaiden.
And more at the link