I think some of the new and last series are amonst the best! You always get the odd one that you think they've lost it a bit with (Sundays in England gwas a good exmple of this). But more often than not it really does have great twists, and presents the questions in a really great way.

I'm guessing that they carried it on partly because of the money, but also because there was more potensial in the new characters, and they still had a lot of good stories left in them. The alian thing never wore thin either