That's going to take some thinking. Warlords Battlecry was pretty new when I bought it, and it came out in 1998, but I think I bought Mario Kart 64 before then. However, I'm not really sure. I'm also trying to remember when I got Pokemon Blue, because it had to have been between 1999 and 2001, right around the same time when I remember buying MK64 and WBC. :/
I'm going to go with Mario Kart 64. I think that was the first game I ever wanted bad enough to actually pay money for it.
First time you can remember getting seriously hurt? (no scraped knees or bloody lips; I want broken bones and torn ligaments here!)