I decided to give it 5 starts instead of 4, only because I enjoyed watching it several times.
Season 1 (Very Good) Pilot Episode was captivating, and makes you want to watch the whole series from episode 1.
Season 2 (The best in television history) Season 2 was the best season by far and way compared to the rest
Season 3 (Very Good) But I would rank it 3rd compared to the first 2 seasons. I wish Lexa, Onya and Lincoln Never Died. I mean seriously the writers messed that up big time, Its ok to kill off characters to improve the story and bring in the desired emotions, but seriously how do you kill Lincoln, well Onya I can understand but she was still cool and Lexa the writers know they made a mistake there because they tried to bring her back in the AI and other flashbacks, think about it, monty, jasper, clarks mom or any of chacellors or even clark would have been better to kill off instead of lincoln or lexa.
Season 4 (Good) But some episode were slightly boring while other episodes were exceptional though. The Good Episodes make up for the rest.
Season 5 (I liked it) But too many people are dying now by the point, If you were going to kill lexa you should have done it in this season at the end but oh well.
Season 6 (I did not like it) I watched it, and still couldn't understand why they went this route, this became problematic for me because every that happened before hand was reasonably possible even if slightly meaning all of it before hand was realistic possibilities, but season 6 took it to a fantasy realm at this point which start to blow it for me and a lot of people agree. You cant travel to another planet in stasis in the number of years they said, there was not even an indication of a theotirtical warp drive to do so, meaning they would not have ever found another planet that could sustain life in a billion years of stasis and simply would have ran out of fuel long before they even got close. When they get to their new world the story becomes kind of bizarre and starts to lose my attention.
Season 7 and I have similar feelings about this season as I did season 6, I did not like the way the show ended either. Finding their way back to earth was a good plot twist, but what people wanted was a sense of peace and nation building to take place. That never happened once in the series, Season 7 went far more into a fantasy realm of star wars star trek type of adventure then the previous seasons 1-5 (Which all were plausibly realistic), meaning the last 2 seasons are like a completely different show to watch altogether.
5 stars because seasons 1-5 were really beyond excellent, but honestly that is where they should have ended it, the final scene should have simply been the crew realizing they found another planet to live on as they awoke from stasis, then End.