I want to see a new Metroid game, a 3D side scroller (or 2.5D, whatever the term is for a 2D game with sharp 3D graphics), with gameplay and tone very reminiscent of Super Metroid. Perhaps a new game in the Prime sub-series, but as I said, a 2D, classic gameplay approach with modern, polished graphics. It would probably work best on the handhelds, ideally the DS. The regular controls can be used, the stylus for aiming and firing--much like in Metroid Prime - Hunters, but in 2D...just tap where the enemy is and Samus shoots in that direction...as long as there are no walls blocking the way, she'll hit her targets. I'd like to see the story continue either after Metroid Prime 3 and before Metroid II - Return of Samus, or after Metroid IV - Metroid Fusion, and have it essentially act as Metroid V.
The chances of another Metroid game are good. Prime 3 just came out, so another major Metroid release for the Wii is probably at least another 2-3 years off. However, a well thought out, faithful to the originals type 2D handheld title could be out as early as next year. There have been rumors about another Metroid game set after Fusion, called Metroid Dread, alleged to be out for te DS. It was debunked as a rumor, then verified again, then debunked again. Hopefully a great 2D Metroid for the DS will become a reality before another 3D FPS.