It's is very well written show and the plot is very well designed. My favourite show. Perfectly matches the science fiction theme. Some people say that the last few seasons are not great and they stretch out, but I disagree. I think they are amazing. I'm not saying they're opinion is wrong or anything. I would rate it a 4.5 though because of the romance (I don't like romance), but that doesn't really change much. I'm up to my 3rd time watching it because its just so good.