Time Traxx screwed up in the first episode, with respect to alternate timeline versus time loop paradoxes, and they still lasted three years. :P
I think nthey're trying to set up a Lost-esque scenario wherein people can COME to the past with all their plot-generating problems, but getting off the island (sic) is basically impossible here. In essence, anyone coming to Terra Nova comes from a Really Bad Place, and they'll deal with them amongst various flesh-eating dinosaurs. They then either resolve their issues and fade away into the local scenery, or be eaten. Rinse and repeat.
As sci-fi setups go, it's not bad. Lots of the less successful sci-fi shows are very closed in their setup and it limits their longevity. For example, Flash Forward, The Event, Heroes, and other recent series start with a very big and traumatic event that propels the world into the story. Thing is, that event never happens again, and the audience is hard-pressed to remember or care why it was that important.
Here, the major event is quickly established as something that will happen again. Everyone got to Terra Nova with a time machine (or whatever), but they won't be the only ones. There WILL be more people coming eventually. Similar to Stargate SG-1, there is a huge plot point in the setup that will remain relevant to everyone for the duration of the show. I think this creates a comfortable place for an audience to visit, and stay interested for the long run. For the sake of the 10 year-old inside me that likes seeing dinosaurs, I hope it will.
Also, the CGI here is as good as stuff on the Discovery Channel. I checked out a dino documentary in the past week (not tought to find, really) and the effects are on par. What creates the difference here is context - it's tough to call a Discovery dinosaur poor quality because you don't have a real human standing next to it. In general, it's no better or worse than what we see in Primeval, and UNLIKE Primeval there seems to be a workable story here.
Mark