Hello Steven
Well for me it's all about characters and good ideas. Some shows had 1 and were good, some had none and were awful but the magic ones were the ones which had both.
I must admit my recent forays into sci-fi on TV have been limited, partly because of the explosion of different channels mean that I can no longer sit with my TV guide and quickly look and see what's on and partly because I find I no longer have the patience to order my life and 'follow' a show on television much these days. So I tend to wait till it's all done and then buy/rent/beg/borrow the dvds and watch them at my own pace and without adverts!
All of which is a bit of a deviation from your original question on favourite shows, so here goes.
Star Trek (TOS) - obvious but a true classic which helped open the doors for so many others. For me, the elements which made it so good were the interaction between the 3 main leads and the ideas it followed. The ideas may seem dated (now) and a little heavy-handed but it combined an important "message" with good comedy and a genuine sense of threat (well, at least when I was little and didn't realise only the ones wearing Red would die!
).
Red Dwarf - the first UK sci-fi show I really got into. Dr Who was cheesy and very dated by the time I was growing up and got cancelled shortly after I turned 11. It was pretty much "The Odd Couple" in space but worked because of that and the characters (A senile supercomputer, A self-absorbed humanoid descended from felines, an anal-retentive hologram with delusions of grandeur and the biggest slob this side of Triton) were genius creations who just complemented each other perfectly.
Hyperdrive was a pale imitation by comparison.
The Twilight Zone - one of my favourite shows of all time precisely because it explored so many ideas. The characters weren't always great and some of the stories seemed to creak under the weight of their 'message' but when it worked it
really worked. One of my favourite moments was the last episode of series 1 (A World of his Own) when Rod Serling makes his first appearance in the series as the narrator.
Firefly - well, what can I say about this show? Possibly the biggest travesty of a cancellation ever. People compared it's cancellation to the original Star Trek but at least Star Trek got 3 series and by it's last series was struggling to recapture it's magic (Spock's Brain - c'mon!). Firefly had it all. Fantastic characters, great running storyline, great recurring villains and one of the best scripts I've ever seen. It's a wonder Josh Whedon didn't find a tall tower near Fox studios and camp there with a sniper rifle waiting for executives. And the worst part is, if a friend hadn't lent me the DVDs (which sat unwatched for 3 weeks on my shelf - a western in space by the maker of Buffy? urgh!) I wouldn't have seen it. Serenity was good, but Firefly was better.
Also honourable mentions for:
Lost in Space
Sliders (well up to series 3 anyway!)
The Time Tunnel
