I'm not going to waste your time with a bunch of preamble to this very straightforward list, but the one caveat I'll make is that there's plenty of shows I loathe but didn't watch a single episode of this year – Two and a Half Men would be the quickest and most obvious example, though nowhere near the only one – and since I want to be honest in my scorn, those shows are exempt from this list. I didn't watch them, so I don't know how bad they were. So, starting with the year's most disappointing show, then its tenth worst and counting down to the biggest televised turd of 2013:
Most Disappointing: Marvel's Agents of S.H.I.E.L.D. (ABC)
# of 2013 episodes watched: 10 (all)

Talk about a show that had every single goddamned thing going for it. Executive producer Joss Whedon, writer/director of The Avengers and more importantly creator of three of the greatest genre shows – hell, shows, period – ever made: Buffy, Angel and Firefly. Showrunners Jed Whedon, Maurissa Tancharoen and Jeffrey Bell, all three late of Spartacus and with Angel and Dollhouse experience under their belts. An already-established sci-fi/fantasy universe lousy with heroes, villains, aliens, monsters, magic, gods, superpowers, alternate dimensions. The enthusiastic backing of their network, money, hype and probably access to any number of fine actors. And with all this we get... NCIS with constant references to the "Battle of New York." Not to mention terrible dialogue, a cast devoid of chemistry or charm, flat, often brutally ugly lighting and cinematography and dull cases that make zero use of this rich universe. I had hoped Agents of S.H.I.E.L.D. could be the new Firefly. Turns out it's the new Studio 60: All hype, nothing there.
10. Under the Dome (CBS)
# of 2013 episodes watched: 13 (all)

Given how angry and frustrated I was with Lost by the end of its run – and if you don't know or forgot, here's a not-so-quick refresher – it's saying something when I call Under the Dome the shitty version of Lost. Not the shitty version of Lost's better seasons, mind you. The shitty version of Lost's already-rotten final season: Dull (and in many cases horribly acted – yes, I'm looking at you, Junior) characters stumbling around a generic genre serial that piled endless vague, riddle-like mysteries on top of each other only to end the season with a jumble of cartoonish nonsense that answered nothing. Under the Dome isn't the worst show on this list, but it may be 2013 TV's finest example of incompetent storytelling.