I'd probably buy one if I used to own one, just for nostalgia. I would buy a Mega Drive (Genesis) and a Master System, but only because I had both as a kid.
One thing they did for the Gamecube was release all the old Sonic games on a single disc, which was cool. They're doing the same thing on Xbox, and I'll definately pick it up as I loved those games when I was a kid (the new 3D Sonic games are an abomination, in my opinion). I do have them all emulated on the PC, but it's not quite the same.
It's odd that I just came across this topic, I've just played Streets of Rage with one of my mates over the internet, we used to play it (and many other Mega Drive games) all the time when we were in primary school.
Xbox Live/PlayStation Network/Steam: tone217
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