It started declining in the late 90s but IMO '99-'07 was by far the worst era of the NBA.
Much of what people today say were the big problems in the 90s were bigger issues in the early 2000s. Heavy isolation play, uber-physical, slow pace, low-scoring games. Throw in the influx of the bad AAU-era players, every player wanting to be the next MJ to disastrous results, too many bad teams blowing picks on crappy HS players. Plus you had all of the original Dream Teamers retiring; there was a huge amount of talent leaving the league and not a ton of it entering the league--especially when it came to big men. And of course, this was the beginning of the chasm between the Eastern and Western Conference that still exists 21 years later.
The original Spurs dynasty was a complete bore, the Pistons weren't much better. The Lakers were fun but it felt like they were cheating since Shaq was the only great center in his prime left in the NBA. The East was an absolute embarrassment. Finals TV ratings went into the toilet. Eventually the league realized how bad things were and made the drastic rule changes in 2005 that have led us to our current era.