It's a little hard for me to say precisely what I want, because I think Nintendo has a lot of options for Metroid this generation which all could have good outcomes. Both Wii U and 3DS are capable of a pretty wide array of play styles, each with about as much merit as the other.
I believe a more traditional Metroid ,in the style of Super Metroid, Zero Mission, etc., is long overdue. Other M tried to at least compromise with those wanting a return to traditional Metroid, but it unfortunately fell short in a couple significant areas which basically left it in a sort of limbo between traditional and new (as opposed to reinventing the series and becoming a play style in its own right, like Metroid Prime did). Were Nintendo to take another crack at Other M's third-person gameplay, vast improvements over Other M would need to be made regarding the exploration and the environments and the story(writing?). The pure gameplay of Other M was actually very well done (save for the first-person segments), and improvements in that area would only be profit. The fact that this style could be achieved on Wii U or 3DS is a bonus as well. Personally, though, as I am an avid lover of 2D platformers, I would like a Super Metroid 2, and on 3DS. Seeing another 3D Metroid in third-person wouldn't break my heart, though, and I think the style has a lot of potential.
I'd also definitely like to see another game in the style of Prime. A couple of conditions of mine, though: 1) Samus is alone throughout most, if not all, of the game; 2) The environments are contained to one planet, or perhaps one main planet with some smaller, extra places such as space stations or moons or asteroids or the like, which could house expansions or minibosses; and 3) I'd prefer the story to be told indirectly, similarly to Metroid Prime. No real reason other than that I like that kind of storytelling and thought it worked well for what Metroid is. A 3D, first-person Metroid which takes full advantage of Wii U--beautiful, vast, full of secrets and adventure--is at the very top of my wishlist for this generation.
A couple of general preferences:
- Multiple interchangeable beam types
- Scanning remains in 3D styles
- No mandatory use of gyroscope
I'm confident Nintendo isn't stupid enough to let this masterpiece of a franchise die out, and I'm excited to see what the generation has in store for Metroid.
P.S. Those who are trying to say 2D gameplay is 'outdated' are silly.