The list of "Top Sci-fi TV shows of all Time" is split into two parts: before 1985, and post-1985. The shows are such different creatures, incredibly different in style, there is no way to compare them. Thus we present 2 list, divided by space and time.
Supernatural is the best horror series , but is excluded from our Sci-Fi list. We wanted a pure science fiction list, futuristic ideas, spaceships and worlds beyond the Earth of today.
First, these are the best Sci-Fi TV Series from 1985 to 2014:
1 - Stargate: Universe (2009) A (third) spinoff from SG1, Universe was an impressive show centered around the space ship Destiny. The moral divergences and change in characters breathed real life into this show. The story was true Sci-Fi, in ways other series have rarely accomplished. It's sad the show was canceled after 2 seasons, despite high ratings. This series was a rare and special treat.
2 - Farscape (1999) The story: phenomenal. The aliens: actually looked like alien creatures, and not just humans with dots and head bumps. The characters were unique, and the writing inspiring.
3 - Star Trek: Next Generation Of course Trek fans rank this as 1, and non-trekkies at 9. Here we place it firmly in third place. The stories, ship and crew are timeless.
4 - Stargate: Atlantis The 2 nd SG1 spinoff exceeded its predecessor by leaps and bounds. The characters are grounded, the writing is brilliant. Surprises in some of the outcomes show an imaginative direction that is too often missing in shows today. "Before I Sleep" was an especially intriguing episode. The show evolved like an usual space chrysalis.
5 - Firefly Unique and entertaining, Firefly was a fantastic space western that was killed off before its time.
6 - Star Trek: Deep Space 9 Of all the Star Trek's, DS9 had the grittiest characters and the some of the best plot lines.
7 - Falling Skies The newcomer on our list is only starting its 3 rd season. The show has paid off well, giving us exactly what we want. More than one race of aliens have invaded earth, and the writing is holding up (so far). Keep fingers crossed.
7/tie - The Expanse. Fabulous space opera from the outer rim.
8 - Primeval (2007) This BBC series had a story arc with a beginning, middle and end. That's rare. It was a brilliantly written series about rips in time, allowing creatures to enter from the prehistoric past... and the dark future. In 2012 a spinoff was made for the US/Canada market called: Primeval New World.
9 - Babylon 5 A stellar space tale; the second show since Blake's 7 to have a continuous story line. Prior to Blake's 7, most series were episodic, including Star Trek. After Blake, B5 took up the helm. In the wake, many continuous, non-episodic, stories were made, like SG Atlantis and Farscape.
10 - Space: Above and Beyond (1995) Only around for 1 season, it was great space combat with good character driven action.
The X-Files might come in at #11, and even though I was a huge X-fan, the show rarely "delivered." It was more of a tease, showing how far a show can go on rumors and maybes, and no pay-offs or special effects. Just one alien would have been gratifying, but it never came, and thus it fails to really be a pure sci-fi show. Supernatural delivers where X-files could not (but in horror).
As for the worst sci-fi tv series: The remade Battleship Galactica (2003 BSG remake) was awful, written for old ladies who like soap operas and more talk than substance. Scrap it for the metal.
Most under-appreciated series: Surface (2005). Another great sci-fi series that was canceled before it could finish. Torchwood and Sliders are also worthy of honorable mention.
Longest-running: Stargate SG-1 (10 seasons), good, but not as good as its 2 spinoffs.
Now step in your time machine, and go back further:
Here are the top Sci-Fi shows before 1985:
1 - Blake's 7 (1978-1981) The first major series to spin a continuous story arc. Not episodic, the story continued from week to week, with characters dying and worlds changing. There was a beginning, middle and end to the serious, much like a multiple-year movie. The show was low on special effects, but high on storytelling. An excellent series that screams for a revival.
2 - Star Trek : Original Series (1966-69) Gene Roddenberry's original Trek was ground-breaking. Bones and Spock are timeless.
3 - Twilight Zone (1959-64) Rod Serling's original show was just that: original! Excellent ideas explored in black and white, with superb acting and writing. Most of today's movies are based on those episodes. Writers have been stealing from TZ for years: the Matrix, Final Destination, Child's Play, Poltergeist, more.
4 - Outer Limits (1963-65) Another original show that's being ripped off today in Hollywood. Great ideas back in the Outer Limits.... We control the horizontal,...
5 - Battlestar Galactica 1978 (original) We stress this listing is for the Original Glen Larson BG. The story was epic, and the Cylons were very cool (voices even cooler). Short-lived due to its expense in a decade of hit (cheap) sitcoms, BG gave us what we needed for a short time.
6 - Dr. Who Possibly the most over-rated show in Sci-Fi, but it does place at mid-point in our list. Uneven in its achievements, between boredom and brilliant, but worthy of placement here.
7 - The Invaders (1967-68) Ray guns and sepia screens, with Suzanne Pleshette to boot!
8 - Jonny Quest (1964) Sure it's an animation, but it kicks butt in the sci-fi story-telling world. The villains, ships, and settings stretched the imagination. Dr. Quest and his crew on the Quest Jet never disappointed. It was violent for its decade; you could count on someone getting murdered in a horrible way every week.
9 - Lost in Space (1965-68) Some inventive effects, very weird stories, and a cliffhanger every week.
10 - Land of the Lost (1974-77) had some of the best writers around, such as Ben Bova, Larry Niven, and Theordore Sturgeon, along with Star Trek's D.C. Fontana. The series was meant for kids on Saturday morning TV, but the stories still hold up today (for adults). The triple moons, the library of skulls, pylons, Enik, the Sleestak, the Zarn...
Planet of the Apes (1974) Mark Lenard (Sarek on Star Trek) played a great General Urko. The series was short-lived, but explored some great ideas beyond the movies. POTA deserves a special runner-up mention for sci-fi TV series.