Most Scifi fans I have ran into can pretty quickly rank the four stars –BattleSTAR Galactica, STAR Trek, STARgate, and STAR wars, but what lesser-known or less-prestigious shows hold a special place in your heart?
Fringe is an excellent show. It begins really episodic, like old school Outer Limits and early X Files. But by third season you're knee deep in a mind-bending larger story arc that absolutely rocks. The finale stands as one of my top 3 series closers. It expertly closes out the show with deep character resolution. And the show as a whole doesn't fall prey to the Lost Mystery Deficit. Mysteries are resolved, and there's great callbacks in final season to the mysteries of season one and two.
Furthermore, the cast is excellent. Joshua Jackson. John Noble pulling off Walter White levels of excellent acting and character change (you'll recognize him as Denethor from Lord of the Rings), and heck, Leonard Nemoy is in it.
If you love sci-fi, you can't go wrong with Fringe.