WCW Thunder made it's debut in 1998 when WCW was the number one promotion in the United States (with the WWF trailing second). At first, I couldn't see how another two hour show could survive given that there was the two/three hour Nitro on Mondays, syndicated programmes and a WCW PPV every month of the year;but Thunder (shown on Thursdays) complimented Monday Nitro very well.
There were some great matches on Thunder during it's early year. However, in late 1998 up until 2001 (when WCW was sold to the WWF), the shows were not very good because the entire WCW product was no good. WCW from late 1998 to March 2001 was a real chore to sit through and was the most confusing and poorly booked wrestling organisation in the world. In March of 2001, it was finally put out of it's misery.
All in all, WCW Thunder was a good show initially. If WCW hadn't become such a crap organisation then I am sure Thunder would still be on today complimenting Monday Nitro very well. If you do decide to track down any episodes of Thunder, then I would recommend looking for 1998 episodes only.