I think what made Metroid Prime a truely unique experience was the solitary nature of the game. It was just you in this beautifully rendered world left by your self, if you ever want a place to collect your thoughts metroid is the game.

Go play Super Metroid.

What made Metroid Prime a truly unique experience was far more than its "solitary nature". There's also the vast exploration, the well-done scanning for info mechanic, the puzzles, the fantastic bosses, getting a new power up and opening up new areas, exploring and unexpectedly finding a small puzzle required to reach a missile expansion, finding a gizmo and going "Hey I know where I can use this!" and making your way to the other side of the world to use it and find a new area, etc.

You could use some expansion on your thoughts.

Also, go play Super Metroid. Seriously. Go play Super Metroid. Like, now.