I have already raved about it as "the greatest science fiction show on television," and many others have sung its praises. Io9.com, for example, calls Fringe "the most daring show" on TV and claims that "the first two hours of Fringe season three make for one of the best science fiction movies" ever seen.
Those of you who have not seen an episode yet might think all of that is over-the-top hyperbole, but tune in and judge for yourself. Some of you may have sampled the show but not stuck around to see all the great payoffs. Catch the first two seasons on DVD to see how the mysteries grow and answers are revealed. Unlike other series that string their audiences along with questions upon questions and no resolutions, Fringe has enough stand alone answers and big reveals to its overarching mythology storyline that it satisfies viewers while keeping them coming back for more.
The alternate universe plot alone makes it worth watching, but there are enough interesting subplots and stand-alone adventures that should keep you entertained season-long.
Maybe I'm overstating how great the show is. Give it a shot and find out.