A few of mine I haven't seen come up in the thread yet:
FlashForward, high concept stuff by Brannon Braga (love him or hate him!), a mysterious event causes everyone on Earth to simultaneously lose consciousness for 137 seconds, during which time people see what appears to be a vision of their own life approximately six months in the future. Lasted 22 episodes and ended on a cliffhanger unfortunately, although the Season 1 story was largely wrapped up.
Terminator: The Sarah Connor Chronicles, a really good TV adaptation of Terminator lore, starred Lena Headley (of GoT fame) and Summer Glau, lasted two seasons and taken from us by the writers strike, just as it was hitting its stride.
Stargate Universe, the SGverse's attempt to do a gritty series. A lot of the fanbase didn't like the darker tone but looking back it was actually pretty good and a lot of modern sci-fi has now gone that way anyway. Robert Carlyle was brilliant. Lasted two seasons and ended on a cliffhanger with the basic mystery lore unresolved.
I was listening to something the other day which pointed out the streaming services (Netflix in particular) have managed to create a vicious circle, because they cancel so much, everyone waits until there's at least 2-3 years and some chance of the story being resolved before they commit to watching. Which in turn means a lot of series get bad figures for the first seasons and get cancelled. And so it goes on.