My wishlist:
- Voiced dialogue with enough story to drive the narrative/mystery.
- Dual-analog (with lock-on) with motion controls supported to refine aiming
- Samus doesn't lose her powers at the beginning of the game because of reasons
- Samus has new weapons/abilities. I'd like a weapon that doesn't feel like a beam or missiles and has a little more of the feel of FPS gunplay.
- An area or space station where I can talk to people, buy stuff, and get enemy bounties to collect. The universe always feels way too small in these games compared to the potential of a "space bounty hunter" concept.
- Some codex that are audio/video recordings that you can listen to (the audio recording mechanic works really well in other games). I like the "get item, rotate it to see more information/explore" too.
- Optional guidance that can be turned off for your traditional Metroid player, but keeps your casual player from getting lost. Maybe Samus talks to an AI in her suit or something?
- Enough action/set-pieces interspersed through the game so that people get their FPS fix
- Some areas we haven't seen before in a Metroid game
- Online multiplayer that has some different feeling classes
There's been lots of examples (Doom, Arkham games, Tomb Raider, Souls series, Mass Effect, etc) that Prime 4 should take some notes from.