I think the 2.5D Nintendo's been doing lately would work well with Metroid. Sprites is great of course, but there are so many cool things you can do with 2.5D when it comes to 3D effects.
Either way I just want another Metroid in its classic style. It's far due for one and after dropping the ball with Other M, the fans deserve a return to form!
Fans want it why won't Nintendo do it? Makes no sense at all some times.