Fellow sci-fi blogger (and apparently a fellow Colcestrian too) Adam Whitehead has been busy with a fascinating and well-written series on the history of the plot arc in sci-fi drama. Part 1, Part 2 and Part 3 of "Arc of Truth" can be read over at the Wertzone and I look forward to Part 4.
Personally I like a good plot arc - I was particularly impressed with the way this was done in the first of the re-launched Doctor Who series: the way the characters returned to the same locations, and the whole series explored the idea that the Doctor's interventions had consequences that played out in the long term after the Tardis had departed.
I've struggled however with the new wave of slow-burning plots - Lost, Invasion, Heroes - with only a trickle-feed of exposition interspersed with hints and tense atmospherics. They can make you feel that, if you miss one episode, you might miss the single key revelation that explains the whole series. I tried with Invasion, I really did - it was such a good first episode I wanted to get into it but it was just too slow.