No it didn't go downhill! Tsk Tsk.
it has always been worth watching, and today it is terrific. Yes, i know some of the plots are hard to follow, but you usually get to make sense of it in the last scene. I love the manic action, the characters, the special effects, the acting, and the whole premise of time travel.
It can be such fun, like the Van Gogh one where they take him into the future to see how his paintings are so loved and so valuable, or the hilarious Torchwood/Queen Victoria one, where Rose tries to get the Queen to say 'We are not amused'. Oh, and 'The Fires of Pompei' was a particularly good one; that one had the new Doctor Who in it too, as a Pompeian.