I agree, "Horizon" has gone a bit down market over the years, but at least it hasn't stooped to the fantasy levels the Discovery and similar channels have moved into. It's still a very educational programme, and does a good job of explaining complex ideas to the general population (which can't be a bad thing in my view).
Other programmes, like the "Do We Need the Moon" one, are also good science, even if a bit vague at times from our viewpoints. For the majority of the public though, they're again great at getting the science across.
Overall, I think the beeb do a pretty good job on science documentaries like these, and hopefully they won't go for the lowest common denom - there are already UK channels who've gone that way...