Genius Programming: The game was way too big to fit on the N64's hardware, so what did Factor 5 do? They used the cartridge itself as ram, essentially streaming the data it needed! Also, instead of using standard microcode (what controlled the graphics hardware), they wrote their own to focus on real-time lighting and high polygon count.
Keep Circulating the Tapes: Said microcode poses a problem today; N64 emulators generally rely on emulating the microcode, instead of the hardware directly, in order to get playable framerates on even high-end systems. That trick doesn't work when the developer throws out the standard libraries from the SDK and rolls their own microcode. Headway has been made in emulating the RSP directly and enabling custom microcode, and indeed some emulators finally can actually boot the game, but currently the only way to actually play is to find a real cart note or shell out big money for a flashcart and drop it into a real console.
What Could Have Been: The game was originally to have been one level longer, with an additional level between Tian Shan River and Shambala Sanctuary called Shambala Waterworks. In the end, the waterworks were merged into a small part of Shambala Sanctuary.