yeah, definitely liked the first metroid prime, i think i maybe got the second one. i like how it was very eerie, just like the rest of the series; very biologically eerie, especially the intro sequence (even before playing the game) and premise, etc.
got to the final boss in metroid 2 just now but died trying to kill it dead.
these 2d games have the thrill of the fight, but what if there was more of a hunt -- like metroids are loose, you have to worry about them "crossing screens" when they come at you, trying to finish you off if you run away. like, you also spot them eating the other critters in the environment (that would be creepy, too). also, maybe if they find them they eat your power ups and you can't get them until you kill them, etc. you could have more of a horror aspect, being chased by them (and chasing them down)?
most later games "fix" this by making it impossible to leave a screen/location when you encounter a boss, but what if they just chased you down instead?