Chiming in late on the SF TV comments -

Eureka was not only a good show consistently through its entire run, but had one of the best final episodes of any series I've ever seen. A real salute to the show, its characters, and actors. The crossovers with Warehouse 13 were fun, too.

Sliders, someone mentioned, started out pretty good, and then season by season, then episode by episode, it got worse until it really stank and I think we gave up on it before the end. Especially replacing cast members one by one until none of the originals remained. I though only Brits did that.