1998 was their last good year. I would stop there if you don't want your mind to explode from all the bullshit that started the following year.
To him, it might not be bullshit. I, myself, feel there were still many good moments post 1998, such as the rise of DDP & Booker T, Bret Hart vs. Chris Benoit, Ric Flair in control of WCW and his feud with Hulk Hogan, great cruiserweight wrestling, Rey Mysterio "the giant killer",great tag team wrestling with Raven/Saturn, the Triad and the West Texas Rednecks/Benoit & Malenko feud, Big Poppa Pump, an entertaining Hardcore division headlined by Norman Smiley and Ralphus and various other moments I'm probably forgetting.
There still were some great moments in WCW, all the way to the end. OP may have different tastes from you. If anything, the bullshit started in mid 2000, after Russo first appeared on camera and is evidenced by the atrocities that occurred from that point on, such as Bash At The Beach 2000, Russo as World Champion, random cage matches on Nitro with no explanation, more celebrity involvement and product placement and the push of Jeff Jarrett. But even with that, you have Booker T, DDP, Mysterio, Kidman & Scott Steiner, who I feel showed enough brilliance that era can be tolerated.