Been using this mod due to enjoying the Metroid soundtrack, but there are some minor issues I have with it (namely, some songs not fitting and there being repeats, the latter of which I will get to last). I'll provide a list (also, sorry in advance if the list sounds kinda ♥♥♥♥♥y)

1. The music that is replacing the Crystal Exploration theme is a combination of 3 songs, the Meridia Swampy Caverns, the Meridia Sandy Desert, and the Crateria Space Pirates theme, since the latter is already used, why not change both the Crystal Exploration themes to be Swampy Caverns for one and Sandy Desert for the other
   
2. I don't know why the final boss theme (Forest Battle 2) had AM2R's Industrial Complex as the boss music. Personally, I think that either the Prime boss theme (since Prime menu is being used as the area's theme) or Mutated Emperor Ing (since you fight the ruin after Asra Nox, who's theme of Arctic Battle 3 is the Emperor Ing music) would be better fits IMHO
   
3. There are several songs that repeat (which I'm sure was mentioned before)*
   
   • Arctic Battle 2 and Arctic Battle 3: Emperor Ing. Replace Arctic Battle 2 (penguin boss music) with Defense Drone from Prime 3.
     
   • Arctic Exploration 1 and Arctic Exploration 2: Submerged Frigate. Replace 1 with Crashed Frigate Entrance
     
   • Crystal Exploration 1 and 2 are already mentioned: replace 1 with Swampy Cavern and 2 with Sandy Desert
     
   • Europa, Forest Loop and Hymn to the Stars: Tallon Overworld (Theme 2). Forest is fine as is. Europa can Sanctuary Fortress Depths while Hymn can be Phendrana Depths
     
   • Forsaken Grotto, Inviolate Loop and Ocean Exploration 2: Lower Norfair. Ocean Exploration is fine, The other two can be replaced with Crateria (Zebes planetfall) and Space Pirate Statue Chamber
     
   • Mercury and The Deep: Chozo Ruins. Since Mercury plays just about everywhere, why not replace it with Multiplayer Theme: Dark Echoes or the Prime 2 credits theme. The Deep is fine as it is.

Anyways, those are just my suggestions, don't have to be added now, just when you have free time.

Edit: Formatting