Thundercats well as Legato has already mentioned the toys didn't sell well because the distribution on them was horrible and not to mention they were made by probably the worst of the mainstream toy companies Bandai America, which is far inferior to it's Japanese counterpart. And of course it was on Cartoon Network which cannot figure how to handle an action series to save it's life; don't believe me just look at how they handled the 4Kids Ninja Turtles, the 2k3 He-Man, Transformers: Animated, Justice League/Unlimited and the way they are currently handling Green Lantern and Young Justice. Even the recent Scooby-Doo series got the bum's rush from Cartoon Network if it's not a comedy or on Adult Swim then an action series is doomed.
All of the recent Marvel cartoons Spectacular Spider-Man, Wolverine and the X-Men and Avengers: Earth's Mightiest Heroes all ended way too soon.
Law & Order is one of those shows that both should have ended a long time ago and could have gone on a lot longer it was all about the casting and the writing and the sad thing is the last two seasons had the best cast and episodes of series in a very long time.
CSI is another series that should have ended after William Peterson left, but the recent season with Ted Danson as the lead character has been very good, but I still feel as though it's time for the series to end.
NCIS is a show that I love but I think it's running out of steam and the sad thing is they already had the perfect ending episode back during Season 3 and I can't see how they'd end the series especially Gibb's story arc better than the ending they gave him in the Season 3 finale.