A decent boxing game, for 1999 standards.
The graphics look really dated and the controls feel a little sluggish, and the music can get really annoying after a while. The fun factor on this one is not specially high.
It has a good array of the most significant real life boxers from all times from the Heavyweight, Middleweight and Lightweight categories, like Muhammad Ali, Rocky Marciano or Sugar Ray, but good old Mike Tyson is missing. You can also create your own boxer and punch your way through the career mode.
In short, Knockout Kings 2000 on the PlayStation was a fairly decent boxing game back in the day, but it has not aged well. With so many good boxing games out there, there is no reason to play this.