Now that you mention the sound, I always had this question: was the GBA sound system any good? My understanding is that the GBA only has the original GB sound chip plus two PCM channels, without any dedicated hardware synthesis or mixing, so all sound effects need to run on software. Now the CPU was so much faster than the SNES or Megadrive, but was it fast enough to make up for it?
GBA games were generally regarded as having lower sound quality than SNES games, although this perception was somewhat exaggerated by the poor quality of some SNES->GBA ports. It took a lot more CPU to get good audio out of the GBA, and I'm sure developers were taking the GBA's tinny speaker into account when deciding how much effort to invest in polishing the soundtrack. Hell, the GBA SP needed an adapter to use headphones!
It has the GB legacy sound and two 8-bit PCM channels (stereo wave output basically). It is definitely worse than the SNES - however, because of how fast the ARM is (relatively speaking) it has no problem doing software mixing to provide developers with effectively 4, 6 and even 8 channels of PCM audio for soundtracks and effects. Not as smooth sound, but totally sufficient.
