the guy who writes meka is heavy into getting all sound emulation perfect including the add-on fm synth proccessor
for the most part, games without fm sound should sound fine
but ones with (japanese version of phantasy star) will usually require tweaking some configs to work correctly
meka is also r e a l l y slow so if you're not sporting a fast processor and a decent video card don't expect the greatest perfomance.
also, if you have a dreamcast, i'd recomend using smeg instead as it runs almost everything perfectly with no extra configuration and it just feels more right playing console games on a console, dunno why