Just finished watching it all. Here are my impressions.
Overall, the casting and acting were very good. All the actors had good chemistry together. Each had their own quirks and personalties and it was just fun to watch. Having to play "double" roles in S3 also showed how good they were, especially Olivia and Astrid.
As for the show itself, it started out great. The first two seasons were very, very good. I looked forward to each new episode. Season 3 was when it started to fade for me. While I thought the acting was great, I just really, really disliked Fauxlivia, and I disliked it even more how they tried to remove the real Olivia at the start. Come Season 4 and the return of a rehashed villain everyone had forgotten about (or two, depending on how you look at it) and you felt that the writers had stopped making an effort. I would never have finished Season 5 had I not been watching with someone who wanted to finish it. I really, really disliked the Observers. Well, I loved the original concept of the observers from the earlier episodes, I disliked how they were turned into superhuman villains. The whole season had that element of depression that so many cancelled shows that still have some episodes left to make have. The only way they could have fixed it was if when Peter put the Observer tech in him he had completely turned into one of them and they through some McGuffin plot element found out he would create the rest of the Observers thereby completing some time loop or whatever. But yeah, having the final episode be some sort of Dallas dream moment where all is returned to normal. Yeah, that was lame.
For those who like Sci-Fi and X-files type stuff, I'd recommend the first 2-3 series, but quit while you're ahead.
