Well in Game Boy Advance i really enjoy:
- Golden Sun 1 & 2
- MegaMan Zero 1, 2, 3 & 4
- Legend Of Zelda A Link To The Past/Four Swords
- Wario Land 4
- Castlevania Aria Of Sorrow
- Final Fantasy Tactics

And none of these games run well on VGBA....MegaMan Zero doesn't even run

For me a 100% working GBA emulator is a must have
GB emulator too, with Pokemon! And iNES just need some tweaks on sound issues, i think!

Also, i don't know if this is possible, but could Bluetooth or Wifi multiplayer be implemented in emulators?