In my case, since I'm a fairly big paleontology buff, and was even more "into" dinosaur science back when Terra Nova was on the air than I even am now, I couldn't forgive the series' really bad depictions of the dinosaurs. Lazy, inaccurate designs, and giving totally incorrect factoids (a "scientist" character on the show describing a carnivorous dinosaur species as having "multiple rows of razor sharp incisors" just....ugh, no.) So the bungling of the dinosaurs was the show's "original sin" and everything else that irked me about it got piled on top of that.
I will give the writers props for one thing though...
One annoying plot point that lasted through the show's entire run was the teenage son of the main character pining for his girlfriend who was still in the future. In like the second to last episode she arrives as part of a subsequent group of colonists. Along with this group come some saboteurs or mercenaries or something, and during the process of a confrontation that ensues shortly after their arrival in the past the girl gets blown up by an IED. I congratulate the writers for having the balls to go that route, and since I hated the teenage boy character so much, the fact that someone he apparently cared about a lot and wouldn't shut up about was vaporized by a bomb also made me smile.

