I would contend that some of the David Tennant episodes are among the best written Sci-Fi to ever make it on TV anywhere (an awesome example is the episode titled
"Blink" which is brilliant and can be enjoyed without ever watching another episode or being a Dr Who fan ... can be found
here as an AVI if you don't have Netflix).
I wouldn't judge the new (since its relaunch in 2005) Dr Who series based on the original series which I really only like for nostalgic reasons ... if I were to watch the old series now for the first time I probably wouldn't like it either.