Keith Courage, Christmas 1990. I knew little-to-nothing about the console, but my Dad got it for me because it was a whopping $20 cheaper than the Genesis at the store he went to. The only things I had seen about it were the cartoon ads for Bonk and Splatterhouse, which I thought were bad ass.
I remember popping in Keith Courage for the first time and thinking it looked pretty awesome graphically. I was a little disappointed by how one-dimensional it seemed, though. No real hidden areas, etc. After playing Super Marios 2 and 3, I was hoping for a bit more depth, I guess.
The only Christmas that topped that one was the year I got a Turbo Duo. Best-Christmas-EVER!