the genesis has a 68000 cpu wich of course is 32bit internally with many registers and many instructions. it also has a z80 cpu which has many registers which can be pared to be 16bit and it has many 16bit instructions.
that is much more complex than an snes which has a fairly simple 65816 16 bit cpu
i think that is what makes the genny much more difficult to emulate. even though the miggy has a 68k you have to emulate the gennys cpu because you have to controle it very precisely to sync everything,
a couple of snes emulators are very playable on 040's genesis ones all need ppc from what ive found now.