AC for gamecube was essentially magic to me as a kid. It required a dedicated memory card, and pretty quickly into playing it I realized that you could eject the disc at the title screen and keep playing. I never looked into it but my guess is that because the game was for n64, the whole thing could fit in the gamecube's ram. Hooking my gameboy and going to the island was also a crazy thing to me.
Once I learned about the post-office item codes online, I started experimenting with the weirder items, and once I got an Action Replay and started doing things like no clipping and generating broken items and NES games, things got even crazier. As a kid, the idea that I could be playing these old NES games was nothing short of magic. It's how I beat punch out as a kid.
It was also super-japanese at a time when those sorts of games never got localized.