Yeah that Space one was scary. I remember a lot of people hated it. I'm actually a real scaredy cat, especially I don't know how I managed to watch it all.
My favourite ones were the funny ones written by Darin Morgan "Jose Chung's From Outer Space" "War of the Cophraphages" and "Clyde Bruckman's Final Repose".
I really liked D.P.O. as well because I was an angry young teenager at the time like the kid with lightening and electrical power.
The ones that really scared me were Humbug (that deformed twin scampering around the ducts really fast, argh), Squeeze and Tooms were pretty bad as well, with a similar theme of someone being able to fit through vents and so on. The episode with the Flukeman was gross and scary, I can't find the name of it though.