If Retro should make a new Metroid game I'd like to see it play like Metroid blast. There should be a co-op aspect just like blast where you are a Wii mote tps, and other player is a space ship. Worlds should be open and arena based. Tight corridors are too oldschool. Lets explore a huge alien Zebus that looks like something from Avatar.
Instead of losing all powers from the begining, you could enchance all your equiptment instead. Hate playing without the rocket jump. Also, co-op should be drop in and out like in Farcry 4. My biggest plea is that Mother Brain is the main vilian again. I hated every end boss since she was absent. Retro sucks at creating their own characters and enemies. Nintendo needs to co-develop the game with Japan. Japan is very good at weird alien creature designs.