I watched the entire series and thought the first season was an amazing, drama/mystery driven by Sci-Fi. Few series have been so well-written: it had me looking in many different directions - spending as much time trying to figure out the mystery as I did getting to know each character, the environment and the hard science (coupled with fictional science). The first season is easily a 10.
The second season went off the rails. I'd rate it a generous 4. While the central premise remained, it shifted toward pseudo-nonsense (I'm trying hard not to give anything away). The storyline wasn't nearly as tightly written (sloppy at times) while everything was forced through a new lens of pure mumbo-jumbo nonsense.
Many of the core characters remained in place, some just disappeared without a proper ending, some secondary characters were given back stories but it was the segue into mumbo-jumbo that did nearly all the harm. The only reason I stayed the course was because of the strength of the first season and to watch the backstories of some of the characters who were given greater roles. I also held out hope that the season would straighten itself out and shift back into Sci-Fi and tighter writing. I was disappointed...
The third season (only four episodes long) shifted back toward "sci-fi science" but the stench of the mumbo-jumbo, pseudo-nonsense hung in the air, intermingling with the stronger premise established in season 1. I'd rate this season a 5 overall. It doesn't quite close the chapter on all characters but does so on most central/core characters. Not sure why this season was only 4 episodes long, certainly the last episode felt rushed but by this point, I was happy to see the series end. I felt that a continuation would further damage one of the best first seasons of any Sci-Fi show I've ever watched.
Recommend watching the first season only (10 rating). The other seasons will disappoint.
Side notes: (1) I had to look this up: Dennis Quaid was 63-64 years old during the last two seasons. I just couldn't get over how much younger (and fit) he looked. (2) Verónica Echegui: great performance, an uncommon beauty. (3) Stanley Tucci: his character helped define the first season and keep it "real" (4) Michelle Fairley: as a GoT fan, nice to see her here (5) Edvin Endre: as a 'Vikings' fan (the Ragnar Lothbrok years only), it was good to see him here too. He's got an "edge" to his acting which comes across very well on screen (6) Robert Sheehan: great in 'Misfits' and 'The Umbrella Academy'. While Stanley Tucci represented a stabilizing force (made the first season smart and adult-driven), Sheehan (sadly) served as the vehicle that knocked 'Fortitude' off the rails and nearly destroyed the series.
