I’d have to say though, I disagree with You on the Visual quality of the games, for Me they are one of the reasons it is so Real, the amount of detail in Structure not so much texture(GCN’s low texture memory) is out of this world!

Everything in Prime games are Visually so sharp & seem to Meld together so well that it has this natural aura like they would in real life, example: playing Halo after Metroid is no longer as realistic because of the fact that although Halo has better textures the level designs just feel artificial, items, large structures such as crates, trees or parts of building architecture etc look and feel like they were placed there by a game designer, when you go throughout the environments in Metroid You will see that most every thing corresponds with one another giving it that Natural & Organic feel, Halo on the other hand does not despite having more texture memory (Xbox).
This shows that there was a lot of care and time put into the Art & Level design department at Retro placing Metroid Prime way ahead of its competitors Artistically.

On top of that, the sound in both games are Frightening to say the least, everything gives off its own distinct Eerily realistic sound, every type of creature, every type of space Pirate, even Samus suit making contact with water, acid, lava, energy beams, plasma swards, Phazon, even the sprays of mist have Incredible visuals & are distinct in sound Lol,
this gives you the feeling that your actually interacting within a Solidified Planet just waiting to be explored.

The way the storyline unravels is in real time so You have to go around looking for information on what happened,
find Lores to discover artifacts & locations or make contact with other lifeforms making it so much more involving than sitting around watching 15min clips spoon feeding You the storyline, not saying I dont like that style but You dont really have to work for it which to Me makes it less involving.

With these elements & many others in place like pacing, difficulty & music makes this game very hard to put down, Scary at times in those most Feared environments, Terrifying as Hell when You have to face those BF Intimidating BOSSES, Gratifying as ever when You finally beat that Hard ass BOSS & pick up that New Weapon or Suit augmentation & absolutely Mind numbing when you think about how much harder its gonna be to get to & Defeat the next BOSS!!!

All in all I can see how this game can make You wanna stray far, far away from it after hours of Breath taking, Mind in numbing, Spine chilling, Blood boiling, Heart pounding Thrills found in the Experience called Metroid Prime/Echos!