I tend to not give a show much chance, if I'm not into it, but shows that were hyped a lot (either by fans or by marketing) and ended up not being worth it to me:
True Blood - cool premise, but I don 't get why each epidose takes so long to get to certain points in the story arc, especially since HBO has no commercials; also the acting was crap, which was another real disappointment from an HBO series.
Bored to Death - a lot of people liked this show, I didn't find it funny
The Shield - after The Wire, it's hard to watch almost any cop show
Lost - trying too hard to make me say "wtf!"
The Borgias - too melodramatic.. could have been a real winner but wasn't.