So the secret sauce was... interesting! Unlike any other company I have seen.
Each game team (of which there were 4 who I was there) was isolated from the other teams, only senior management and IT had access to the other team's floors/buildings. If someone from another team needed to visit for some reason we were usually instructed to turn off monitors. There was very little sharing of code and core graphics/gameplay features were fiercely protected by each team. The competition was not other games companies (with the exception of Nintendo) but the team in the next building.
There was almost no recruiting from other games studios, almost everyone was hired out of college (or recently so).
The management (Tim and Chris) generally let the teams do what they thought best and didn't push hard on things like deadlines. Release dates existed but were argued/negotiated with Nintendo when things slipped.
Employees were expected to be in the building at 9am (there was a bonus for punctuality, which I dint think I ever received and was reprimanded about several times). Lunch and dinner were provided, the studio was literally on a farm so there were no lunchtime distractions, and long hours were expected, although not mandated. 70+ hour weeks were not unusual.
Teams got a small bonus for shipping a game but then got a split of game sales (after some 'production cost' was subtracted). The split increased as Rareware negotiated higher payments from Nintendo, for later N64 games the team received something insane like $1 per cartridge, which on a 10-16 person team with millions of sales was crazy money. People were paying cash for houses and Porsches.
Unfortunately while the generous bonuses drove the work culture, it also caused a large amount of resentment. People on shelved projects, projects on low royalty rates (eg Goldeneye), or poor selling products put in the same or more work but did not anywhere near the same fiscal rewards. It was a side effect of Tim and Chris being extremely generous and wanting to do the right thing by the staff but it did cause a number of departures (albeit mostly from the Goldeneye team), I think this has been discussed publicly by many of those folks.