The last great Sega Console was the dreamcast. It is still
legendary for its perfect arcade ports. this was possible
due to the fact that the Naomi Arcade board was the same as the
DC but with more memory
There is no good Dreamcast emulator for the Mac yet. Still
LXDream, a Linux based Dreamcast
emulator is working on OSX support (probably intel
macs only though). If oyu have an intel Mac, you could
consider booting up in XP.
A nice blog with lots of things about the Dreamscast is
the Dreamcast Junkyard
My personal favourite games are.
* Samba de Amigo
Rhytm based and lovely
* Crazy Taxi
Great Arcade port of taxi simulator
* Gigawing, important shoot'em up that redressed the
balance between player and enemy. See here for more details
* Densha de Go, Arcade train
simulator