When Retro Studios put the finishing touches to Metroid Prime 3: Corruption, it stated that it would be the final game in the series. The announcement of Metroid: Other M - which is being handled by Tecmo's Team Ninja - seemed to confirm this, despite the recent repackaging of all three Prime games in Metroid Prime Trilogy.
However, in a recent interview with Kotaku, Japanese producer Kensuke Tanabe seemed to indicate that there's life in the franchise yet. When questioned about the multiplayer aspects of future Metroid titles (not specifically those in the Prime series, it should be noted), Tanabe uttered these words:
As all I take part in is the Prime series, I am not capable of commenting on the whole Metroid series. But we will keep considering multiplayer for the Prime series. For instance, I think I can come up with some unique ideas using the Morph Ball, which is a specific skill of Samus.
Was this a case of misunderstanding the question or are Nintendo currently working on more Prime instalments?
While you're chewing over that little glimmer of hope, why not check out the entire interview, which sees Retro Studios look back on the Metroid Prime series. It's a top-notch read.