By completing this game and using the GBA/GCN link cable, one could unlock the original NES game Metoroido (1986).
Metroid: Fusion (2002) was chronologically the last of the Metroid games until Metroid Dread (2021).
The idea for the Fusion Suit arose after members of the development team felt that the design of Samus' suit has become stale. Because the team felt that a drastic change to such an iconic character could ruin them, chief director Yoshio Sakamoto encouraged them to include an in-universe explanation for it.
SR388, the native world of the Metroids, is most likely a reference to LV-426, the planetoid on which the derelict spacecraft was found in the original Alien: Das unheimliche Wesen aus einer fremden Welt (1979).